JP7325778B2 - Method for producing low-molecular-weight polytetrafluoroethylene, composition, and low-molecular-weight polytetrafluoroethylene - Google Patents

Description

The present disclosure relates to methods for producing low molecular weight polytetrafluoroethylene, compositions and low molecular weight polytetrafluoroethylene.

Low-molecular-weight polytetrafluoroethylene (also called "polytetrafluoroethylene wax" or "polytetrafluoroethylene micropowder") with a molecular weight of several thousand to several hundred thousand has excellent chemical stability and extremely low surface energy. In addition, since fibrillation is unlikely to occur, it is used as an additive to improve the lubricity and the texture of the coating film surface in the production of plastics, inks, cosmetics, paints, greases, etc. (see, for example, Patent Document 1). .

As methods for producing low-molecular-weight polytetrafluoroethylene, a polymerization method, a radiation decomposition method, a thermal decomposition method, and the like are known. Conventionally, in radiolysis, low-molecular-weight polytetrafluoroethylene is generally obtained by irradiating high-molecular-weight polytetrafluoroethylene with radiation in an air atmosphere.

In addition, methods for reducing perfluorocarboxylic acids and salts thereof that may be produced as a by-product of radiolysis are also being investigated (see Patent Documents 2 and 3, for example).

JP-A-10-147617 WO2018/026012 WO2018/026017

An object of the present disclosure is to provide a method for producing low-molecular-weight polytetrafluoroethylene that does not easily generate perfluorooctanoic acid and salts thereof.
Another object of the present disclosure is to provide a novel low-molecular-weight PTFE composition and low-molecular-weight PTFE with a low content of perfluorooctanoic acid and salts thereof.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, comprising a substance capable of generating free hydrogen atoms. a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of The present invention relates to a method for producing low-molecular-weight polytetrafluoroethylene, which includes the step (2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating the moieties.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, comprising a substance capable of generating free hydrogen atoms. Step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of A low-molecular-weight polytetrafluoroethylene comprising the step (2a) of obtaining the low-molecular-weight polytetrafluoroethylene by heating or heat-treating at a temperature equal to or higher than the room temperature transition temperature of tetrafluoroethylene (19° C., which is the _β1 dispersion temperature) It also relates to a method for producing ethylene.

The heating or heat treatment in step (2a) is preferably carried out at a temperature of 70°C or higher.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, comprising a substance capable of generating free hydrogen atoms. Step (1) for reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of It also relates to a method for producing low-molecular-weight polytetrafluoroethylene, including the step (2b) of obtaining the low-molecular-weight polytetrafluoroethylene by maintaining the above.

It is preferred that the holding in step (2b) is performed for 10 hours or more.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, comprising a substance capable of generating free hydrogen atoms. a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of It also relates to a method for producing low-molecular-weight polytetrafluoroethylene, comprising step (2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating the moieties, and carrying out steps (1) and (2) simultaneously.

The substance capable of generating free hydrogen atoms is preferably at least one selected from the group consisting of hydrocarbon-based organic compounds, amines, silane-based organic compounds, water and hydrogen.

The substance capable of generating free hydrogen atoms is at least one selected from the group consisting of chain hydrocarbon compounds, cyclic hydrocarbon compounds, synthetic polymers, biodegradable polymers, carbohydrates, ammonia and water. is also preferred.

The amount of the substance capable of generating free hydrogen atoms is preferably 0.0001 to 1000% by mass relative to the high-molecular-weight polytetrafluoroethylene.

Preferably, the dose of radiation in step (1) is 10-1000 kGy.

It is also preferred that the dose of radiation in step (1) is 100-750 kGy.

It is preferred to carry out step (1) substantially in the absence of oxygen.

It is preferred to carry out step (2) substantially in the absence of oxygen.

It is preferred to maintain substantially oxygen-free conditions during the period from the beginning of step (1) to the end of step (2).

The high molecular weight polytetrafluoroethylene preferably has a standard specific gravity of 2.130 to 2.230.

Both the high-molecular-weight polytetrafluoroethylene and the low-molecular-weight polytetrafluoroethylene are preferably powders.

The production method further includes a step (3), prior to step (1), of obtaining a molded article by heating the high-molecular-weight polytetrafluoroethylene to a temperature equal to or higher than its primary melting point, and the molded article has a specific gravity of is preferably 1.0 g/cm ³ or more.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, wherein the sample temperature during irradiation with radiation is High molecular weight in the presence of a substance capable of generating free hydrogen atoms under conditions of room temperature transition temperature (19 ° C., which is the _β1 dispersion temperature) of fluoroethylene and 320 ° C. or lower, and a dose rate of 0.1 kGy / s or higher. The present invention also relates to a method for producing low-molecular-weight polytetrafluoroethylene, characterized by comprising the step (X) of obtaining the low-molecular-weight polytetrafluoroethylene by irradiating the polytetrafluoroethylene with radiation.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380°C of 1.0 × 10 ² to 7.0 × 10 ⁵ Pa·s, wherein the melt viscosity at 380°C is 1.0 Polytetrafluoroethylene of ×10 ² to 7.0×10 ⁵ Pa·s is irradiated with radiation in the presence of a substance capable of generating free hydrogen atoms, thereby reducing the molecular weight of the polytetrafluoroethylene. a step (Y1); and a step (Y2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating at least part of the main chain radicals and terminal radicals generated by the irradiation. It also relates to a method of making molecular weight polytetrafluoroethylene.

The present disclosure includes low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, and a substance capable of generating free hydrogen atoms, It also relates to compositions in which the content of octanoic acid and its salts is less than 25 ppb by weight.

In the above composition, the content of perfluorooctanoic acid and its salt, which is determined according to the heating/measurement condition A described below, is preferably less than 100 mass ppb.

In the above composition, it is also preferable that the content of perfluorooctanoic acid and its salt determined according to the heating/measurement condition A is less than 50 mass ppb.

In the above composition, it is also preferable that the content of perfluorooctanoic acid and its salt determined according to the heating/measurement condition A is less than 25 mass ppb.

In the above composition, the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof is preferably less than 25 mass ppb.

In the above composition, the total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof is preferably less than 25 mass ppb.

In the present disclosure, the melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, and the peak obtained by electron spin resonance measurement under vacuum satisfies the following relational expression (I): The content of perfluorooctanoic acid and its salts is less than 25 mass ppb, and the content of perfluorooctanoic acid and its salts determined according to the heating and measurement conditions A described later is less than 100 mass ppb. It also relates to molecular weight polytetrafluoroethylene.
Relational expression (I): 3.0>Peak M/Peak A>0.3
(In the formula, Peak M represents the peak height at the center of the triplet corresponding to the terminal radical in the low-molecular-weight polytetrafluoroethylene, and Peak A represents the peak height of the double quintet corresponding to the main chain radical in the low-molecular-weight polytetrafluoroethylene. represents the peak height.)

In the present disclosure, the melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, and the peaks obtained by electron spin resonance measurement in the atmosphere are represented by the following relational expressions (1) and (2) is satisfied,
A low-molecular-weight polytetrafluorooctanoic acid and a salt thereof having a content of less than 25 mass ppb and having a content of perfluorooctanoic acid and a salt thereof less than 100 mass ppb determined according to the heating and measurement conditions A described later. It also relates to fluoroethylene.
Relational expression (1): Peak M2/Peak A1≧1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak A1 represents the intensity on the main chain of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the negative peak intensity corresponding to the alkyl-type peroxide radical trapped in ).
Relational expression (2): Peak M2/Peak M3<1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak M3 represents the molecular-chain end of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the positive peak intensity corresponding to the peroxide radical trapped in ).

(Heating/measurement condition A)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
The content of perfluorooctanoic acid and its salts is measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile is added to 1 g of the heated sample, and ultrasonic treatment is performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase is measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous ammonium acetate solution (20 mmol/L) (B) are fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) is used, the column temperature is 40° C., and the injection volume is 5 μL. ESI (Electrospray ionization) Negative is used as the ionization method, the cone voltage is set to 25 V, and precursor ion molecular weight/product ion molecular weight is measured to be 413/369. The content of perfluorooctanoic acid and its salts is calculated using the external standard method.

In the present disclosure, the melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, and the standard value obtained by the following formula (3) is 1.1 to 10.0, It also relates to low molecular weight polytetrafluoroethylene having a content of perfluorooctanoic acid and its salts of less than 25 mass ppb.
Formula (3):
Standard value = (absorbance of the functional group derived from the hydrogenated product of the low-molecular-weight PTFE) / (hydrogenation of the low-molecular-weight PTFE obtained by irradiation in the absence of a substance capable of generating free hydrogen atoms) absorbance of functional groups derived from the body)

The low-molecular-weight polytetrafluoroethylene preferably contains less than 25 mass ppb in total of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof.

The low-molecular-weight polytetrafluoroethylene preferably contains less than 25 mass ppb in total of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof.

According to the present disclosure, it is possible to provide a method for producing low-molecular-weight polytetrafluoroethylene that hardly produces perfluorooctanoic acid and salts thereof.
In addition, according to the present disclosure, it is also possible to provide a novel low-molecular-weight PTFE composition and low-molecular-weight PTFE with a low content of perfluorooctanoic acid and its salts.

FIG. 2 is a diagram showing an example of peaks obtained by electron spin resonance (ESR) measurement under vacuum; FIG. 2 is a diagram showing an example of peaks obtained by electron spin resonance (ESR) measurement in the atmosphere;

When high-molecular-weight PTFE is irradiated with radiation under conventional conditions, low-molecular-weight PTFE is produced, and at the same time, a perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof may be produced as a by-product. These by-product compounds include perfluorooctanoic acid with 8 carbon atoms or salts thereof, of perfluorocarboxylic acid, or a salt thereof.
In addition, main chain radicals and terminal radicals generated by irradiation with radiation at room temperature substantially in the absence of oxygen react with oxygen in the air by heating after irradiation, thereby producing C 4-14 radicals. Perfluorocarboxylic acid or its salts, especially perfluorooctanoic acid or its salts may be produced.
The present inventors irradiate the above high molecular weight PTFE with radiation in the presence of a substance capable of generating free hydrogen atoms, and deactivate the radicals generated by the irradiation to obtain perfluorooctanoic acid and its salts, and further , found that the production of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof is suppressed, and completed the production method of the present disclosure.
The present disclosure will be specifically described below.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, comprising a substance capable of generating free hydrogen atoms. a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of The present invention relates to a method for producing low-molecular-weight polytetrafluoroethylene, which includes the step (2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating the moieties.

In step (1), the high molecular weight PTFE is reduced in molecular weight by irradiating the high molecular weight PTFE with radiation in the presence of a substance capable of generating free hydrogen atoms.
It is believed that the reduction in molecular weight is achieved by cutting the main chain of the high-molecular-weight PTFE due to the radiation irradiation.

The radiation is not particularly limited as long as it is ionizing radiation, and includes electron beams, gamma rays, X-rays, neutron beams, high-energy ions, etc. Electron beams, gamma rays, or X-rays are preferred for industrial use. , electron beams or gamma rays are more preferred.
An electron beam can be generated, for example, from an electron accelerator.
Gamma rays can be generated, for example, from radioisotopes.
X-rays can be generated, for example, by irradiating a target such as a metal with a particle beam from a particle accelerator. In addition, quasi-monochromatic X-rays can be generated by inverse Compton scattering (laser Compton scattering) by colliding a laser beam with a high-energy electron beam. Furthermore, X-rays can be generated by synchrotron radiation, or X-rays can be generated by installing an undulator or wiggler in the lower stage of the particle accelerator.

The absorbed dose of the radiation is, for example, preferably 10 kGy or more, more preferably 100 kGy or more, still more preferably 150 kGy or more, even more preferably 200 kGy or more, and 250 kGy or more. is particularly preferred, and 300 kGy or more is most preferred. The absorbed dose is preferably 1000 kGy or less, more preferably 750 kGy or less, and even more preferably 500 kGy or less.
The above numerical range can be suitably employed, for example, in irradiation at room temperature (25° C.).
Radiation irradiation may be performed continuously until a desired absorption dose is reached, or may be performed intermittently and repeatedly until a desired absorption dose is reached in total.
By setting the absorption dose within the above range, the molecular weight of the high-molecular-weight PTFE can be reduced even in the absence of oxygen. The absorbed dose is preferably optimized according to the target molecular weight.

The absorbed dose rate during irradiation of the above radiation is not particularly limited, but for example, for gamma rays emitted from cobalt 60, etc., it is preferably 0.1 kGy/h or more, more preferably 1 kGy/h or more, and 2 kGy/ h or more is more preferable.
The electron beam from the electron accelerator is preferably 0.1 kGy/s or more, more preferably 1 kGy/s or more, and still more preferably 10 kGy/s or more. Alternatively, it is preferably 0.1 kGy/pass or more, more preferably 1 kGy/pass or more, and even more preferably 10 kGy/pass or more.
X-rays generated by irradiating a target for X-ray generation with a particle beam from a particle accelerator, particularly an electron beam from an electron accelerator, is preferably 0.1 kGy/s or more, more preferably 1 kGy/s or more, 10 kGy/s or more is more preferable. Alternatively, it is preferably 0.1 kGy/pass or more, more preferably 1 kGy/pass or more, and even more preferably 10 kGy/pass or more.

It is preferable to irradiate the radiation so that the reaction occurs uniformly over the entire PTFE sample and that the absorption dose distribution is uniform. For example, in the case of γ-rays from cobalt 60, the penetrating power of γ-rays is attenuated by the square of the distance. Therefore, if the thickness of the sample is large, a distribution of γ-rays is generated on the front and back surfaces irradiated with γ-rays. Therefore, it is preferable to periodically invert or rotate the PTFE sample. However, if the sample is particularly thick, even if it is turned over, a dose distribution of about 20% to 30% may occur between the outer periphery and the center. It is preferable to devise the distribution and irradiation shape.
In the case of an electron beam from an electron accelerator, the depth of penetration varies depending on the acceleration voltage of the electrons/the acceleration energy of the electrons on the sample surface. It is preferable to take measures such as reducing the thickness to the following and periodically inverting the sample.
Furthermore, in the case of X-rays generated by irradiating an X-ray generation target with an electron beam from an electron accelerator, the X-ray penetrating power attenuates with the square of the distance. A distribution occurs on the front and back surfaces illuminated by the line. Therefore, it is preferable to periodically invert or rotate the PTFE sample. However, if the sample is particularly thick, even if it is turned over, a dose distribution of about 20% to 30% may occur between the outer periphery and the center. It is preferable to devise the distribution and irradiation shape.

The temperature of the sample in the radiation irradiation is not particularly limited as long as it is above the γ dispersion temperature near -80°C and below the melting point of high molecular weight PTFE. It is also known that the molecular chains of high-molecular-weight PTFE are crosslinked near the melting point, and in order to obtain low-molecular-weight PTFE, the temperature is preferably 320°C or lower, more preferably 310°C or lower, and even more preferably 300°C or lower. Although it is economically preferable to irradiate in a temperature range from normal temperature to about 50° C., in order to increase the efficiency of decomposition by radiation, the temperature may be raised for irradiation.
In addition, the sample temperature may change between -80°C and 320°C while the irradiation is continued.

Examples of combinations of sample temperature and absorbed dose during irradiation are shown below, but are not limited to these.
The absorbed dose of the above-mentioned radiation, when irradiated at −80° C., is preferably 100 kGy or more, more preferably 200 kGy or more, still more preferably 250 kGy or more, and most preferably 300 kGy or more. . The absorbed dose is preferably 1200 kGy or less, more preferably 1000 kGy or less, and even more preferably 800 kGy or less.
The absorbed dose of the above radiation, when irradiated at 50° C., is preferably 60 kGy or more, more preferably 120 kGy or more, still more preferably 140 kGy or more, and most preferably 160 kGy or more. The absorbed dose is preferably 700 kGy or less, more preferably 600 kGy or less, and even more preferably 500 kGy or less.
The absorbed dose of the above radiation at 100° C. is preferably 50 kGy or more, more preferably 100 kGy or more, still more preferably 120 kGy or more, and most preferably 150 kGy or more. The absorbed dose is preferably 600 kGy or less, more preferably 500 kGy or less, and even more preferably 400 kGy or less.
The absorbed dose of the above-mentioned radiation is preferably 40 kGy or more, more preferably 80 kGy or more, still more preferably 100 kGy or more, and most preferably 120 kGy or more when irradiated at 150°C. The absorbed dose is preferably 550 kGy or less, more preferably 450 kGy or less, and even more preferably 350 kGy or less.
The absorbed dose of the above radiation at 200° C. is preferably 30 kGy or more, more preferably 60 kGy or more, still more preferably 80 kGy or more, and most preferably 100 kGy or more. The absorbed dose is preferably 500 kGy or less, more preferably 400 kGy or less, and even more preferably 300 kGy or less.
The temperature at the time of radiation irradiation is measured by measuring the temperature of the atmosphere in which the process is carried out with a thermocouple, platinum resistor, etc., or by measuring the temperature of the sample surface or inside the sample with a thermocouple, platinum resistor, etc. method, or a method of measuring infrared radiation from the sample surface with an infrared radiation thermometer, or the like.

Irradiation in step (1) is carried out in the presence of a substance capable of producing free hydrogen atoms. Free hydrogen atoms generated from the above material during irradiation react with main chain radicals and terminal radicals generated by irradiation of high-molecular-weight PTFE to capture the radicals. Therefore, the reaction between the main chain radical and the terminal radical and oxygen can be suppressed, and the formation of perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt, particularly perfluorooctanoic acid and its salt can be suppressed. It is considered possible.

The substance capable of generating free hydrogen atoms is not particularly limited as long as it is a substance capable of generating free hydrogen atoms upon exposure to radiation. The substance is preferably a compound capable of generating a free hydrogen atom. The substance may be solid, liquid, or gaseous, but is preferably solid in terms of ease of handling and vacuum deaeration in the container. The state of the above substance is the state at 25° C. and 1 atm.
Free hydrogen produced by irradiation with radiation can be obtained by a gas chromatography method, for example, K.K. Takashika, et al. , Radiat. Phys. Chem. 55, p. 399-408 (1999) and T. Seguchi, et al. , Radiat. Phys. Chem. 85, p. 124-129 (2013).

Examples of substances capable of generating free hydrogen atoms include hydrocarbon-based organic compounds, amines, silane-based organic compounds, water, and hydrogen.

The hydrocarbon-based organic compound has at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a silicon atom and a halogen atom (chlorine atom, bromine atom, etc.). good too.

Examples of the hydrocarbon-based organic compounds include chain hydrocarbon compounds, cyclic hydrocarbon compounds, synthetic polymers, biodegradable polymers, carbohydrates, and the like.
Examples of the chain hydrocarbon compound include acetylene, paraffin, and the like. The paraffin may have more than 20 carbon atoms.
Examples of the cyclic hydrocarbon compounds include aromatic compounds such as benzene, cumene, toluene, xylene, aniline and naphthalene; and alicyclic hydrocarbon compounds such as cyclopropane and cyclohexane.
Examples of the synthetic polymer include polyolefins such as polyethylene and polypropylene; aromatic hydrocarbon polymers such as polystyrene, polyhydroxystyrene and polyaniline; alicyclic hydrocarbon polymers such as cycloolefin polymers, and the like.
Examples of the biodegradable polymer include polylactic acid; polycaprolactone; polyglutamic acid; polypeptides; proteins such as collagen and keratin.
Examples of carbohydrates include monosaccharides such as glucose; polysaccharides such as cellulose and starch.
The molecular weight of the chain hydrocarbon compounds, cyclic hydrocarbon compounds and monosaccharides may be less than 2000, and may be less than 1000.
The synthetic polymer, biodegradable polymer and polysaccharide may have a molecular weight of 2000 or more.
As used herein, the molecular weight of a substance capable of generating free hydrogen atoms can be obtained by calculation from chemical formulas or by gel permeation chromatography (GPC). In addition, the molecular weight and molecular weight distribution width can be directly measured by MALDI ToF-MS, which is a combination of Matrix Assisted Laser Desorption Ionization and Time of Flight Mass Spectrometry. can.

Among the above hydrocarbon-based organic compounds, paraffin, synthetic polymers, biodegradable polymers, and carbohydrates are preferred, and paraffins, polyolefins, aromatic hydrocarbon polymers, biodegradable polymers, and carbohydrates are more preferred. Aromatic hydrocarbon polymers, biodegradable polymers, and polysaccharides are more preferred, polyethylene, polylactic acid, and cellulose are even more preferred, and polyethylene is particularly preferred.

Examples of the amines include ammonia, primary amines, secondary amines, tertiary amines, etc. Among them, ammonia is preferred.
The molecular weight of the amines may be less than 1000.

Examples of the silane-based organic compound include silane, alkoxysilane, tetraethyl orthosilicate, polysiloxane, and derivatives thereof, with polysiloxane being preferred.
The polysiloxane and its derivative may have a molecular weight of 1,000 or more, and the silane-based organic compound other than the polysiloxane and its derivative may have a molecular weight of less than 1,000.

One or more of the substances capable of generating free hydrogen atoms can be used.

Substances capable of generating free hydrogen atoms include hydrocarbon-based organic compounds, amines, silane-based organic compounds, water and hydrogen in that perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof can be more efficiently reduced. It is preferably at least one selected from the group consisting of, more preferably at least one selected from the group consisting of hydrocarbon organic compounds, amines and water, chain hydrocarbon compounds, ring It is more preferably at least one selected from the group consisting of hydrocarbon compounds of the formula, synthetic polymers, biodegradable polymers, carbohydrates, ammonia and water, polyolefins, aromatic hydrocarbon polymers, biodegradable polymers , polysaccharides, ammonia and water, more preferably at least one selected from the group consisting of polyethylene, polylactic acid and cellulose, more preferably at least one selected from the group consisting of polyethylene is particularly preferred.
The substance capable of generating free hydrogen atoms is preferably at least one selected from the group consisting of polyolefins, aromatic hydrocarbon polymers, biodegradable polymers, polysaccharides, ammonia, water and hydrogen.
The substance capable of generating free hydrogen atoms is also preferably a hydrocarbon-based organic compound. Among them, polyolefin such as polyethylene can be used in the form of polymer pellets and contains many hydrogen atoms in the main chain, so compared to other substances, it is particularly preferable in that it is practically excellent in handling. .

The form of the substance capable of generating free hydrogen atoms is not particularly limited, and may be block, pellet, powder, sheet, strand, or the like.

The amount of the substance capable of generating free hydrogen atoms is preferably 0.0001 to 1000% by mass with respect to the high molecular weight PTFE. The amount of the substance is more preferably 1% by mass or more, still more preferably 2% by mass or more, particularly preferably 10% by mass or more, and 150% by mass of the high-molecular-weight PTFE. % or less, more preferably 100 mass % or less, even more preferably 50 mass % or less, and particularly preferably 25 mass % or less.
When the amount of the above substance is within the above range, the perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt can be reduced more efficiently.

When the substance capable of generating free hydrogen atoms is a polymer compound (molecular weight of 1000 or more), the amount thereof is preferably 0.1 to 1000% by mass, preferably 1% by mass or more, relative to the high molecular weight PTFE. More preferably, it is more preferably 5% by mass or more, particularly preferably 10% by mass or more, and more preferably 100% by mass or less, and 50% by mass or less. More preferably, it is particularly preferably 25% by mass or less.

When the substance capable of generating free hydrogen atoms is a low-molecular-weight compound (molecular weight less than 1000), the amount thereof is preferably 0.0001 to 100% by mass, preferably 0.001% by mass, relative to the high-molecular-weight PTFE. % or more, more preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and more preferably 100% by mass or less, 50% by mass % or less, and particularly preferably 10 mass % or less.

The above-described amount of substances capable of generating free hydrogen atoms is the amount present in the space (container) in which step (1) is performed.

In step (1), the high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms may or may not be in direct contact with each other.

Step (1) may be carried out substantially in the absence of oxygen, and as described later, may be carried out in the presence of oxygen. is preferred.

As used herein, substantially free of oxygen means that the oxygen concentration in the atmosphere in which the process is carried out is less than 2.0% by volume. The oxygen concentration is preferably 1.0% by volume or less, and less than 1.0% by volume, in that the production of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof can be further suppressed. is more preferably 0.5% by volume or less, even more preferably 0.1% by volume or less, and particularly preferably 0.01% by volume or less. The lower limit of the oxygen concentration may be a value below the detection limit. Note that the main component gas at this time may be an inert gas. Examples of the inert gas include nitrogen gas, argon gas, helium gas, mixed gases thereof, and the like. Nitrogen gas is preferable for industrial use.
The oxygen concentration can be determined by analyzing the atmosphere in which the process is carried out, for example, a gas phase portion in a container in which the high-molecular-weight PTFE is placed, by gas chromatography, using an oxygen concentration measuring device, or It can be easily measured by a method of examining the color tone of the oxygen detector.

Moreover, the environment in which step (1) is carried out may be under pressure, under atmospheric pressure, or under reduced pressure. A reduced-pressure environment is preferable from the viewpoint of safety measures for the working environment due to the generation of cracked gas in step (1). The decompressed environment referred to here means an environment degassed to a degree of vacuum of 100 Pa or less by a vacuum pump such as a diaphragm pump, an oil rotary pump, or a scroll pump. The degree of vacuum is preferably 10 Pa or less, more preferably 1 Pa or less, in that the production of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof can be further suppressed.
As a method for maintaining the reduced-pressure environment during the step (1), a sealed container for reduced pressure may be used, or the reduced-pressure environment may be maintained while constantly evacuating the container with a vacuum pump. The pump may be cycled on and off to maintain a reduced pressure environment within the container.
Oxygen adsorbents may be used to remove oxygen present in the environment, resulting in a substantially oxygen-free environment. An oxygen absorber is also called an oxygen scavenger and is synonymous. Of course, the oxygen adsorbent may be used in combination with the above method. As a method of combined use, in addition to placing the oxygen adsorbent together with the high-molecular-weight PTFE in the sealed container, the inside of the sealed container may be uniformly or unevenly coated with the oxygen adsorbent. .

Examples of the method of performing step (1) in the substantial absence of oxygen include a method of performing step (1) in a space substantially free of oxygen.

The space substantially free of oxygen means a space in which the oxygen concentration can be locally adjusted during the steps (1) and (2).
For example, a container that can be sealed so as to adjust the oxygen concentration in the internal space (hereinafter referred to as a closed container) can be used.
Alternatively, the space in which step (1) and step (2) are performed may be locally made substantially free of oxygen by gas shower with an inert gas or differential evacuation with a vacuum pump system.
In addition, as a method of maintaining a state in which oxygen is substantially absent in the above step (1) using an inert gas, a sealed container may be used, or an inert gas may be maintained while circulating. Alternatively, the flow of the inert gas may be intermittently turned on and off repeatedly.

The closed container may be connected to a pipe for sucking and discharging an inert gas or the like described later, or for discharging the gas in the closed container. Other pipes, lids, valves, flanges, etc. may be connected. Moreover, the shape is not particularly limited, and may be cylindrical, prismatic, spherical, or the like, and may be a bag with a variable internal volume. Also, the material thereof is not particularly limited, and may be metal, glass, polymer, a composite material obtained by laminating them, or the like. The closed container preferably has a material and structure that allows radiation to pass therethrough and is not deteriorated by exposure to radiation, but is not limited thereto. Moreover, the closed container is not limited to a pressure-resistant container.

In the above airtight container, materials for bags with variable internal volume include rubber materials that can be sealed by physical stress, such as ethylene-propylene rubber, tetrafluoroethylene-propylene rubber, chloroprene rubber, and polyester elastomer, as well as heat-resistant materials. It is preferable to use a material that can be sealed by fusion or an epoxy-based adhesive. Among them, a thermoplastic organic material that can be sealed by heat sealing is particularly preferable. Among the above thermoplastic organic materials, polyesters such as polyethylene terephthalate (PET), polyamide (PA), polyethylene (PE), polyamideimide (PAI), thermoplastic Polyimide (TPI), polyphenylene sulfide (PPS), polyetherimide (PEI), cyclic polyolefin (COP), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE) , hexafluoropropylene-tetrafluoroethylene copolymer (FEP), perfluoroalkoxyalkane (PFA) and the like are preferred. In addition, these materials may be multi-layer film materials such as two-layer or three-layer film materials, or may be organic and inorganic composite multi-layer film materials combined with aluminum foil or the like.

A state in which substantially no oxygen exists in the closed container can be achieved, for example, by making the inside of the closed container substantially vacuum or filling the inside of the closed container with an inert gas. Here, "substantially vacuum" means that the pressure in the container is 100 Pa or less, preferably 50 Pa or less, more preferably 10 Pa or less.

The inert gas must be inert to the reaction of reducing the molecular weight of high-molecular-weight PTFE by irradiation and to the main chain radicals and terminal radicals generated by the irradiation. Examples of the inert gas include gases such as nitrogen, helium, and argon. Among them, nitrogen is preferred.

The inert gas preferably has an oxygen content of less than 2.0% by volume, more preferably 1.0% by volume or less, even more preferably less than 1.0% by volume. It is even more preferably 0.5% by volume or less, even more preferably 0.1% by volume or less, and particularly preferably 0.01% by volume or less. The lower limit is not particularly limited, and may be an amount below the detection limit. When the content of oxygen in the inert gas is within the above range, the perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt are more difficult to form.
The oxygen content can be confirmed by gas chromatography analysis, galvanic cell type oxygen concentration meter, zirconia type oxygen concentration meter, oxygen detection paper, and the like.

The oxygen adsorbent is not particularly limited as long as it has a function of adsorbing oxygen. An adsorbent exhibiting a known oxygen adsorption effect, such as an organic oxygen adsorbent such as activated carbon, can be used. The oxygen adsorbent may be of the moisture-dependent type that requires moisture when reacting with oxygen or the self-reacting type that does not require moisture, but the self-reacting type is preferable. As the oxygen adsorbent, an iron-based self-reacting oxygen adsorbent, quicklime, or the like is preferable, and an iron-based self-reacting oxygen adsorbent is particularly preferable.

When step (1) is carried out substantially in the absence of oxygen, the production method of the present disclosure includes, prior to step (1), substantially adding the high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms to It is preferable to include the step of charging into a closed container in the absence of oxygen.
As a method of introducing the high-molecular-weight PTFE into a closed container substantially in the absence of oxygen, for example, after placing the high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms in the closed container, A method of putting an oxygen adsorbent into the closed container according to the above, and vacuum degassing the inside of the closed container; and a method of charging at least one selected from the group consisting of these into the closed container, combined use of these methods, and the like.

More specifically, after placing the high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms in the closed container, the inside of the closed container is evacuated to a reduced-pressure environment by a vacuum pump, and the closed container is A vacuum degassing method for sealing, placing the high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms in the closed container, evacuating the closed container as necessary, and then evacuating the closed container The gas replacement method of filling with the inert gas, and further, the method of making substantially oxygen absent by repeating the vacuum degassing method and the gas replacement method, etc., or the high molecular weight PTFE and the free hydrogen are placed in the closed container. A gas circulation replacement method, etc., in which a substance capable of generating atoms is placed and the inert gas is continuously circulated in the closed container to gradually lower the oxygen concentration to create a desired substantially oxygen-free environment. are mentioned.
When the oxygen adsorbent is used, the high-molecular-weight PTFE, the substance capable of generating free hydrogen atoms, and the oxygen adsorbent are placed in the closed container in air, and then the closed container is sealed. a method of placing the high-molecular-weight PTFE, the substance capable of generating free hydrogen atoms, and the oxygen adsorbent in the closed container, degassing the inside of the closed container, and sealing the closed container; The high-molecular-weight PTFE, the substance capable of generating free hydrogen atoms, and the oxygen adsorbent are placed in a closed container, and if necessary, the inside of the closed container is vacuum deaerated, and then the inside of the closed container is filled with the inert gas. A method of filling with gas and the like can be mentioned.

Step (1) may be carried out in the presence of oxygen, for example, in the air, as long as it is in a closed container. In this case, the oxygen concentration in the closed container may be 2.0% by volume or more. The reason why it is possible to suppress the formation of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof even in the presence of oxygen is not clear, but in a closed container, the above-mentioned free hydrogen atoms are generated during irradiation. It is presumed that the oxygen is consumed by the reaction of a part of the substance capable of reacting with oxygen, and the reaction between the main chain radical or the terminal radical and the oxygen is suppressed.
As the closed container in this embodiment, the same closed container that can be used when the step (1) is carried out substantially in the absence of oxygen can be used. It is preferable to determine the size and content of the sealed container in consideration of the amount of oxygen consumed by the substance capable of generating free hydrogen atoms.

Step (1) may be carried out by adding a halogen-containing material. The halogen-containing material in this case may be solid, liquid, or gaseous. Fluorinated oil is preferable as the halogen-containing material.

Step (1) consists essentially of a saturated hydrocarbon having 1 to 20 carbon atoms, a chlorinated saturated hydrocarbon having 1 to 18 carbon atoms, a monohydric saturated alcohol having 1 to 12 carbon atoms, and It is preferably carried out in the absence of a saturated monocarboxylic acid having 1 to 13 carbon atoms.
Step (1) is also preferably carried out substantially in the absence of n-hexane, 3-methylpentane and ethanol.
The fact that the substance is substantially absent means that the amount (total amount) of the substance present is less than 0.1% by mass relative to the high-molecular-weight PTFE. The abundance is preferably less than 0.001% by mass, preferably 0.0005% by mass or less, and more preferably 0.0001% by mass or less. Although the lower limit is not particularly limited, it may be an amount below the detection limit.

In step (2), the low-molecular-weight PTFE is obtained by inactivating at least part of the main chain radicals and terminal radicals generated by the irradiation.
When high-molecular-weight PTFE is irradiated with radiation, main chain radicals (alkyl radicals) and terminal radicals of PTFE are generated. Here, the term "main chain radical" refers to a radical formed at a portion other than the end of the PTFE main chain, and the term "terminal radical" refers to a radical formed at the end of the PTFE main chain. The above-mentioned main chain radicals and terminal radicals are radicals generated immediately after irradiation with radiation in the presence of the substance capable of generating free hydrogen atoms, and they react with oxygen to form peroxide radicals. is different.
The present inventors have found that when these radicals, particularly the radicals generated at the ends of the main chain (terminal radicals) react with oxygen, a perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof is generated. Ta.
In the step (2), at least part of the generated and trapped radicals, particularly the terminal radicals contributing to the generation of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof, are deactivated to remove the perfluorocarboxylic acid. The low-molecular-weight PTFE can be obtained with almost no acid or salt thereof produced.

In step (1), when the high-molecular-weight PTFE is irradiated with radiation in the presence of the substance capable of generating free hydrogen atoms, the high-molecular-weight PTFE is reduced in molecular weight to generate the main chain radicals and terminal radicals, Free hydrogen atoms are generated from the above substances. Then, the main chain radical and the terminal radical react with the free hydrogen atom and are captured by the free hydrogen atom, thereby deactivating the main chain radical and the terminal radical. Therefore, in the manufacturing method of the present disclosure, step (2) is also performed by performing step (1). Therefore, there is no need to perform the step of deactivating the main chain radicals and the terminal radicals in equipment separate from the irradiation, and the manufacturing cost of the equipment can be reduced.
However, in order to further promote deactivation of the main chain radical and the terminal radical, in step (2), at least one step of steps (2a) to (2c) described later may be performed, and step (2a ) and (2b), or step (2a). Even if these steps are carried out, they can be carried out under relatively mild conditions, so that the production cost can be reduced.
Further, step (1) and step (2) may be repeated a plurality of times. However, when performing multiple times, it is essential to end with step (2), which is the step of deactivating terminal radicals.

Step (2) is preferably carried out substantially in the absence of oxygen. It is also preferable to maintain a substantially oxygen-free state during the period from the start of step (1) to the end of step (2).
The state in which oxygen is substantially absent is as described above, and the oxygen concentration in the atmosphere in which the process is carried out must be less than 2.0% by volume, and not more than 1.0% by volume. is preferably less than 1.0% by volume, more preferably less than 0.5% by volume, even more preferably 0.1% by volume or less, and 0.01% by volume or less is particularly preferred. The lower limit of the oxygen concentration may be a value below the detection limit.

From an industrial process point of view, it is preferable to carry out step (2) while maintaining the environment in step (1).

Step (2) is preferably carried out in a space substantially free of oxygen.
Step (2) may be performed in the same space as step (1), or may be performed in a different space.
In order to reliably prevent contact between the low-molecular-weight product and oxygen and to simplify the process, the low-molecular-weight product is subjected to step (2) while being held in the space where step (1) was performed. is more preferable.
Moreover, step (2) may be performed continuously as a series of steps with step (1).
When step (2) is performed in a space different from step (1), the low-molecular-weight product obtained in step (1) is placed in the space in which step (2) is performed in the absence of oxygen. The transfer may be performed, or, as described later, under predetermined conditions, the transfer may be performed in the atmosphere.

When step (1) is carried out in a closed container in the presence of oxygen, it is preferable to subject the obtained low-molecular-weight product to step (2) while being held in the closed container in which step (1) was carried out. .

In step (2), for example, the low-molecular-weight product obtained in step (1) is heated or heat-treated at a temperature equal to or higher than the room temperature transition temperature of PTFE (19° C., which is the _β1 dispersion temperature), It is preferable to carry out the step (2a) of obtaining the low-molecular-weight PTFE (hereinafter also referred to as accelerated deactivation process). According to this aspect, the radical can be deactivated in a relatively short time.
The low-molecular-weight product is a substance generated by cutting the main chain of the high-molecular-weight PTFE due to the radiation irradiation in step (1), and has main chain radicals and terminal radicals generated by the irradiation.
The half-life time of radical deactivation at room temperature of alkyl radicals and terminal radicals on the main chain generated and trapped in PTFE is 1000 hours (literature Radiat. Phys. Chem., Vol 50 (1997) pp601-606), Radical deactivation is accelerated by heating.

Step (2a) is preferably carried out substantially in the absence of oxygen. Conditions in which oxygen is substantially absent are as described above.

The heating or heat treatment in step (2a) is performed at a temperature equal to or higher than the room temperature transition temperature ( _β1 dispersion temperature) of PTFE. The room temperature transition temperature ( _β1 dispersion temperature) of PTFE is 19°C.
The temperature of the heating or heat treatment is preferably PTFE's room temperature transition temperature ( _β2 dispersion temperature) (30°C) or higher, more preferably 70°C or higher, still more preferably 100°C or higher, and particularly preferably 140°C or higher. Also, the temperature is preferably 310° C. or lower, more preferably 300° C. or lower, and still more preferably 260° C. or lower.
However, since it is possible to adopt relatively mild conditions as described above, the temperature of the heating or heat treatment may be, for example, less than 150°C or 100°C or less.
The temperature at the time of heating or heating is determined by measuring the temperature of the atmosphere in which the process is performed using a thermocouple, platinum resistor, etc., or by measuring the temperature of the surface or inside the sample using a thermocouple, platinum resistor, etc. It can be easily measured by a method of measuring, or a method of measuring infrared radiation from the sample surface with an infrared radiation thermometer.
The sample temperature may vary between -80°C and 340°C during step (2a).

The time for the heating or heat treatment depends on the heating or heating temperature, but for example, it is preferably 1 minute or more, more preferably 10 minutes or more, and further preferably 1 hour or more. It is preferably 4 hours or more, particularly preferably 4 hours or more, preferably less than 100 hours, more preferably 50 hours or less, and even more preferably 30 hours or less.
The heating or heat treatment time is the time after the entire sample reaches a state of thermal equilibrium.
The above time range is particularly suitable for heat treatment at 150° C., for example.

The method of heating or heat treatment is not particularly limited, but a method using equipment capable of artificially applying heat is preferable, and examples thereof include a method using the following heat treatment apparatus. For example, box dryer, band dryer, tunnel dryer, jet dryer, moving bed dryer, rotary dryer, fluidized bed dryer, flash dryer, box dryer, disk dryer, cylindrical agitator Dryer, inverted conical stirring dryer, microwave device, vacuum heat treatment device, box type electric furnace, hot air circulation device, flash dryer, vibration dryer, belt dryer, extrusion dryer, spray dryer, infrared heater, etc. be.

The heating or heat treatment is performed, for example, by placing the low-molecular-weight substance held in a predetermined space (e.g., the closed container used in step (1), the closed container into which the low-molecular-weight substance was transferred) in a heating furnace. It can be carried out by placing it in a heating furnace, raising the inside of the heating furnace to a desired temperature, and leaving it for a desired period of time.
When carrying out the step (2a), it is preferable to use a container capable of transferring heat inside and outside as the closed container. The closed container is preferably a container having sufficient heat resistance to withstand the above warming or heating. Heat resistance is not essential.
Materials for the closed container include rubber materials such as ethylene-propylene rubber, tetrafluoroethylene-propylene rubber, chloroprene rubber, and polyester elastomer that can be sealed by physical stress, as well as heat-sealing and epoxy-based adhesives. A material that can be hermetically sealed with an agent is preferred. Among them, a thermoplastic organic material that can be sealed by heat sealing is particularly preferable. Among them, polyesters such as polyethylene terephthalate (PET), polyamide (PA), polyamideimide (PAI), thermoplastic polyimide (TPI), polyphenylene sulfide (PPS), Polyetherimide (PEI), polypropylene (PP), cyclic polyolefin (COP), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), hexafluoropropylene-tetrafluoro Ethylene copolymer (FEP), perfluoroalkoxyalkane (PFA) and the like are preferred. In addition, these materials may be multi-layer film materials such as two-layer or three-layer film materials, or may be organic and inorganic composite multi-layer film materials combined with aluminum foil or the like.

Step (2a) can also be carried out in the presence of water. The water is preferably water vapor. The amount of water is preferably less than 20% by mass, more preferably less than 15% by mass, still more preferably less than 10% by mass, and 0.00001% by mass with respect to the high-molecular-weight PTFE. It is preferably 0.0001% by mass or more, and more preferably 0.0001% by mass or more.

In step (2), the step (2b) of obtaining low-molecular-weight PTFE by holding the low-molecular-weight product obtained in step (1) for 5 minutes or longer (hereinafter also referred to as a spontaneous deactivation process) is performed. may be implemented. In this embodiment, the radicals (especially the terminal radicals) are deactivated by holding the low-molecular-weight product for a specific period of time. The radicals can be deactivated without
The low-molecular weight product is as described above.
Although step (2b) may be maintained by artificially controlling the temperature, it is preferably carried out without using equipment capable of artificially applying heat.
After performing step (2b), step (2a) may be performed.

Step (2b) is preferably carried out substantially in the absence of oxygen (the low-molecular-weight product is maintained in an environment substantially free of oxygen for a specific period of time). Conditions in which oxygen is substantially absent are as described above.

In step (2b), the temperature of the environment in which the low-molecular-weight product is maintained is preferably a temperature that can be achieved without using equipment capable of artificially applying heat. The temperature is preferably equal to or higher than the room temperature transition temperature of PTFE ( _β1 dispersion temperature) (19° C.) in that the time required for radical deactivation can be shortened, and the room temperature transition temperature of PTFE ( _β2 dispersion temperature) ( 30° C.) or higher, and more preferably 40° C. or higher.
Also, the temperature may be less than 100°C or less than 70°C.
The sample temperature may vary between -20°C and 100°C during step (2b).

In step (2b), the retention time of the low-molecular-weight product is 5 minutes or more. When step (1) and step (2b) are performed continuously, the above time shall represent the time from the end of the irradiation.
The time in the step (2b) is preferably 10 minutes or longer, more preferably 1 hour or longer, still more preferably 10 hours or longer, and even more preferably 1 day or longer, It is even more preferably 50 hours or longer, even more preferably 100 hours or longer, and particularly preferably 200 hours or longer.

As a method for carrying out step (2b), for example, there is a method in which the low-molecular-weight product obtained in step (1) is left in the space used in step (1) for the above time.
The leaving can be performed in a warehouse, a greenhouse, or the like, for example.
Here, the greenhouse includes a building such as a sunroom constructed with daylighting glass, a greenhouse for agricultural use, and the like, which is not equipped with equipment for actively heating and controlling the temperature.

In step (2), step (2c) of reacting the low-molecular-weight product obtained in step (1) with a substance having radical scavenging ability can also be carried out. According to this aspect, the radicals can be deactivated in a relatively short time without heating or heat treatment. Heating or heat treatment can also be carried out together.
However, since free hydrogen atoms generated from the substance capable of generating free hydrogen atoms used in step (1) have radical scavenging ability, step (2c) may not be performed in the production method of the present disclosure. preferable.
In addition, the step (2a) may be performed after the step (2c) is performed, or the steps (2c) and (2a) may be performed at the same time.
The low-molecular weight product is as described above.

Step (2c) is preferably carried out substantially in the absence of oxygen. Conditions in which oxygen is substantially absent are as described above.

The substance having radical scavenging ability is a substance capable of deactivating the main chain radicals and terminal radicals generated in step (1). The substance having radical scavenging ability may be a gas having radical scavenging ability. The gas should be gaseous at 25° C. and 1 atm.
Hydrogen gas and halogen gas are preferable as the gas having the radical scavenging ability.
Examples of the halogen gas include fluorine gas, chlorine gas, bromine gas, and iodine gas.
In addition, alkane gas, alkene gas, alkyne gas, fluoroalkane, tetrafluoroethylene, carbon monoxide, nitrogen monoxide, nitrogen dioxide, water, amines, alcohols, ketones, etc. and the like.
The substance having radical scavenging ability may be a substance capable of generating a free hydrogen atom. Specific examples of the substance capable of generating the free hydrogen atom are as described above.
The substance having radical scavenging ability may be a substance different from the substance capable of generating free hydrogen atoms used in step (1).

Examples of the alkane gas include methane, ethane, propane, and butane.
Examples of the alkene gas include ethylene, propylene, and butene.
Examples of the alkyne gas include acetylene, monovinylacetylene, and divinylacetylene.
Examples of the fluoroalkane include difluoromethane, trifluoromethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, and the like.
Water as the gas having the ability to scavenge radicals may be water vapor. For example, it may be water vapor generated by heating liquid water or treating it with ultrasonic waves, but it is not limited to this.
Examples of the water include ion-exchanged water, distilled water, hard water, soft water, tap water, etc., but ion-exchanged water and distilled water are preferable because impurities are less likely to be mixed into the low-molecular-weight polytetrafluoroethylene.
The above water may be water generated from the oxygen adsorbent, or may be water obtained when the water adsorbed by the silica gel is evaporated by heat.
Ammonia etc. are mentioned as said amines.
Examples of the alcohols include methanol, ethanol, isopropanol and alcohol derivatives.
Examples of the ketones include acetone and benzophenone. One or more of the gases having the ability to scavenge radicals may be used.
Further, the above gas may be used by mixing with an inert gas such as nitrogen or carbon dioxide.

Gases having the ability to scavenge radicals include hydrogen gas, halogen gas, alkane gas, alkene gas, alkyne gas, fluoroalkane, tetrafluoroethylene, carbon monoxide, nitrogen monoxide, nitrogen dioxide, water, amines, alcohols and It is also preferably at least one selected from the group consisting of ketones, hydrogen gas, fluorine gas, chlorine gas, bromine gas, iodine gas, alkane gas, alkene gas, alkyne gas, fluoroalkane, tetrafluoroethylene, It is also preferably at least one selected from the group consisting of carbon oxide, nitrogen monoxide, nitrogen dioxide, water, amines, alcohols and ketones, and at least one selected from the group consisting of hydrogen gas and water. is also preferred, hydrogen gas is preferred, and water is also preferred.

In the reaction in step (2c), for example, the substance having radical scavenging ability is introduced into the space (for example, the closed container used in step (1)) in which the low-molecular weight product is held, or the space is circulated. After degassing with a vacuum pump, the substance having radical scavenging ability is introduced, and the low-molecular-weight substance and the substance having radical scavenging ability are brought into contact with each other.
After the concentration of the substance having the radical scavenging ability is balanced in the space, the introduction may be stopped by closing the valve with a valve or the like, or the substance may be constantly circulated.

Further, when a closed container made of a material containing hydrogen atoms is used as the closed container for carrying out the step (1), a radiolytic gas containing hydrogen gas as a main component is generated from the closed container during radiation irradiation. The decomposition gas may be used as the substance having radical scavenging ability in step (2c). Further, when a sealed container made of a material containing halogen atoms is used, halogen gas is also generated as radiolysis gas in addition to hydrogen gas. The decomposition gas may be used as the substance having radical scavenging ability in step (2c).
As the material containing hydrogen atoms, organic materials containing hydrogen atoms are preferable, and rubber materials containing hydrogen atoms such as ethylene-propylene rubber and polyester elastomer; polyesters such as polyethylene terephthalate (PET), polyamide (PA), and polyethylene. (PE), polyamideimide (PAI), thermoplastic polyimide (TPI), polyphenylene sulfide (PPS), polyetherimide (PEI), cyclic polyolefin (COP) and other thermoplastic organic materials containing hydrogen atoms. .
As the material containing a halogen atom, an organic material containing a halogen atom is preferable, and rubber materials containing a halogen atom such as tetrafluoroethylene-propylene rubber and chloroprene rubber; polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer (ETFE ), polychlorotrifluoroethylene (PCTFE), hexafluoropropylene-tetrafluoroethylene copolymer (FEP), perfluoroalkoxyalkane (PFA) and other thermoplastic organic materials containing halogen atoms.

When hydrogen gas is used as the substance having the radical scavenging ability, a molecular structure containing hydrogen atoms and a molecular chain containing double bonds are formed inside the obtained low-molecular-weight PTFE, and the low-molecular-weight PTFE and hydrogen atoms are formed. Compatibility with different kinds of organic substances is improved.

The concentration of the substance having radical scavenging ability to be introduced should be 0.1% by volume or more. Preferably, it is 3% by volume or more, more preferably 10% by volume or more. When the concentration of the substance having radical scavenging ability is increased, the radical deactivation time is shortened.
Substantially, in step (1), the total number per gram of main chain radicals (alkyl radicals) and terminal radicals generated and captured immediately after irradiation, or they are exposed to the atmosphere and generated by reacting with oxygen The number of atoms or molecules having radical scavenging ability should be 1% or more, preferably 5% or more, and more preferably 10% or more, relative to the total number of peroxide radicals per gram.

The temperature for the above reaction is preferably γ dispersion temperature of PTFE (near −80° C.) or higher, more preferably _β1 dispersion temperature (19° C.) or higher, still more preferably 25° C. or higher, and _β2 dispersion temperature (30° C.). The above are particularly preferred.
The sample temperature may vary between -80°C and 380°C during step (2c).

The reaction time is preferably 30 minutes or longer, more preferably 1 hour or longer, after the concentration of the substance having radical scavenging ability reaches equilibrium in the reaction space.

Steps (2a), (2b) and (2c) may be carried out individually or in any combination thereof.
Each of steps (2a), (2b) and (2c) is preferably carried out after step (1), and preferably carried out continuously after step (1).

In the step (2), the deactivation of the terminal radical can be confirmed by the presence or absence of a triplet signal by measurement at room temperature using an electron spin resonance apparatus (ESR). When the above triplet signal cannot be clearly detected by measurement at room temperature (25° C.), it is determined that the terminal radical is deactivated. In the step (2), the terminal radicals are preferably deactivated to such an extent that the triplet signal cannot be clearly detected by ESR measurement at room temperature (25° C.).
Similarly, the deactivation of the main chain radical can be confirmed by a decrease in the signal intensity of the double quintet or the presence or absence of the signal by measurement at room temperature using an electron spin resonance apparatus (ESR). When the double quintet signal cannot be clearly detected, it is determined that the main chain radical has been deactivated. In step (2), deactivation of the main chain radical is preferably carried out to such an extent that a double quintet signal cannot be clearly detected by ESR measurement at room temperature (25° C.).
On the other hand, deactivation occurs when residual radicals react with atmospheric oxygen to form peroxide radicals on the main chain (alkyl-type peroxide radicals) and terminal peroxide radicals (terminal-type peroxide radicals). can be confirmed by the decrease in the intensity of the signal corresponding to those peroxide radicals or the presence or absence of the signal. Based on the symmetry and asymmetry of the spectrum measured by the ESR apparatus, it is possible to distinguish between the main chain type (asymmetric) and terminal type (symmetric) peroxide radicals. If it is difficult to distinguish by room temperature measurement, it can be clearly distinguished by lowering the temperature and performing measurement at the liquid nitrogen temperature of 77K.
After confirming the deactivation of the main chain radical and the terminal radical based on the triplet and double quintet signals by the ESR measurement described above, the alkyl type peroxide radical and the terminal type peroxide radical were obtained when the low molecular weight PTFE sample was exposed to the atmosphere. In addition, it is thought that main chain radicals and terminal radicals slightly remaining in the sample below the detection sensitivity of the ESR device react with oxygen in the atmosphere. In addition, when irradiation is performed in the presence of oxygen as in the conventional method, the above-mentioned alkyl-type peroxide radicals and terminal-type peroxide radicals are generated, but most of the observed radicals are terminal-type peroxide radicals. is.
Double quintet and triplet ESR signals have a wider sweep width than peroxide radicals, and the S/N ratio with the baseline is worse than that of peroxide radicals. However, when it is changed to peroxide radicals by exposure to air, an ESR signal may be detected.

In step (2), when performing at least one step (also referred to as step (2′)) of steps (2a) to (2c), from the end of step (1) to the start of step (2′) During the period, it is preferable not to substantially react the low-molecular-weight product obtained in step (1) with oxygen. This can further reduce the amount of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof. The reaction between the low-molecular weight product and oxygen as used herein means the reaction between the main chain radical and/or the terminal radical in the low-molecular weight product and oxygen, particularly the reaction between the terminal radical and oxygen.
Not allowing the low-molecular-weight substance to substantially react with oxygen means, as described below, that the amount of oxygen that can come into contact with the low-molecular-weight substance is controlled to a very small amount, or that the low-molecular-weight substance and oxygen means that the contact with is carried out under very limited conditions.

In the production method of the present disclosure, a substantially oxygen-free state is maintained during the period from the start of step (1) to the end of step (2′), that is, from the start of step (1) During the period until the end of step (2′), the oxygen concentration in the atmosphere is preferably maintained at less than 2.0% by volume, more preferably at 1.0% by volume or less, and 1.0% by volume. more preferably maintained at less than 0.5% by volume, even more preferably maintained at 0.5% by volume or less, even more preferably maintained at 0.1% by volume or less, even more preferably maintained at 0.01% by volume or less. Especially preferred. The lower limit of the oxygen concentration may be a value below the detection limit. This makes it possible to further suppress the reaction between oxygen and the main chain radicals and terminal radicals generated by the irradiation of radiation, and further reduce the amount of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof generated. can.

As a method for maintaining a substantially oxygen-free state during the period from the start of step (1) to the end of step (2′), for example, step (1) and step (2) are carried out in the same sealed container. During the period from the start of step (1) to the end of step (2′), the closed container is not opened, and the space is maintained by periodically degassing the space with a vacuum pump or the like. a method of periodically circulating an inert gas in the space; a method of periodically degassing the inside of the sealed container with a vacuum pump or the like and circulating the inert gas repeatedly;

In addition, the sealed container in which step (1) was carried out is opened in a space substantially free of oxygen, and the low-molecular-weight product is transferred to another sealed container used in step (2′) in the same space. A method is also included. As the method, for example, the sealed container in which step (1) was performed is opened in a container such as a glove box filled with an inert gas or the like, and another container used in step (2') is opened in the same space. For example, a method of transferring the low-molecular-weight product to a closed container to maintain an oxygen-free state.

In the manufacturing method of the present disclosure, step (1) and step (2′) may be performed in different spaces (preferably, in different closed containers).
According to this aspect, it is possible to adopt the optimum space (closed container) in each of the steps (1) and (2′). In particular, in step (2′), it is possible to adopt a heat-resistant sealed container or a pressure-resistant sealed container that can more effectively perform heating, heating, pressure reduction, and the like. As a result, the amount of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof can be more easily reduced. The above aspect is particularly useful when step (2') is step (2a).

In the production method of the present disclosure, the low-molecular-weight product obtained in step (1) is removed from the space where step (1) was performed under conditions in which the low-molecular-weight product and oxygen do not substantially react. ') may be included.
The transfer of the low-molecular-weight product is preferably carried out substantially in the absence of oxygen. However, it can also be carried out in the atmosphere under conditions in which oxygen does not substantially react with the terminal radicals of the low-molecular-weight products that tend to induce perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof. From the industrial process point of view, it is more advantageous to carry out in the air.

Conditions under which the terminal radicals in the low-molecular-weight substance do not substantially react with oxygen include, for example, a contact time of 180 minutes or less between the low-molecular-weight substance and the air, and 60 minutes or less. is preferred. The lower limit of the contact time may be 1 second.
Also, the temperature of the atmosphere with which the low-molecular-weight compound is brought into contact may be set to 30° C. or lower, preferably 19° C. or lower. The lower temperature limit may be -196°C.

Further, in the manufacturing method of the present disclosure, when step (2′) is repeated multiple times, or when a plurality of steps (for example, steps (2a), (2b), etc.) are performed as step (2′), Between one step and the next step, the low-molecular-weight product may be exposed to the atmosphere (for example, transferred to another container in the atmosphere). It would be advantageous in terms of industrial processes if it could be exposed to the atmosphere (open to the atmosphere) between steps. After the radicals have been deactivated to some extent (especially after the radicals have been deactivated to some extent by performing the step (2b) after the step (1)), even if exposed to the atmosphere, the carbon number immediately 4-14 perfluorocarboxylic acids and their salts do not increase.
In the above embodiment, it is particularly preferable to carry out step (2b), then carry out atmospheric exposure, and then further carry out step (2′) (preferably step (2a)).

In the production method of the present disclosure, the low molecular weight product obtained in step (1) is held at a temperature of 19 ° C. or higher for 5 minutes or more in a substantially oxygen-free space as step (2b). After quenching at least a portion of the terminal radicals in the sample, from within the space in which steps (1) and (2b) were performed, into the substantially oxygen-free space in which step (2′) is performed, in air. It is preferred to include the step of transferring.
In the production method of the present disclosure, the low molecular weight product obtained in step (1) is treated in a substantially oxygen-free space as step (2b) for 1 hour or more at a temperature of 19 ° C. or higher. a substantially oxygen-free space in which step (2′) is performed from within the space in which steps (1) and (2b) were performed after at least some of the terminal radicals in the sample are deactivated by holding It is more preferable to include the step of exchanging in the atmosphere.
In the production method of the present disclosure, the low molecular weight product obtained in step (1) is held at a temperature of 19 ° C. or higher for one day or more in a substantially oxygen-free space as step (2b). After quenching at least a portion of the terminal radicals in the sample, from within the space in which steps (1) and (2b) were performed, into the substantially oxygen-free space in which step (2′) is performed, in air. It is further preferred to include the step of transferring.
The longer the time (time of step (2b)) in which the low-molecular-weight product is maintained at a temperature of 19° C. or higher in a substantially oxygen-free space, the greater the proportion of terminal radicals that are deactivated. As a result, the time during which the low-molecular-weight product can be exposed to the atmosphere becomes longer.

When the above-described step (2′) is repeated multiple times, or when multiple steps are performed as step (2′), the air exposure time between steps can be, for example, 10 days or less, It is preferably 7 days or less, more preferably 3 days or less. The lower limit of the above time may be 1 second or 5 minutes.
Also, the temperature of the atmosphere with which the low-molecular-weight compound is brought into contact can be 40° C. or lower, preferably 30° C. or lower, and more preferably 19° C. or lower. The lower temperature limit may be -196°C.

In the production method of the present disclosure, steps (1) and (2) described above may be performed simultaneously, or steps (1) and (2′) may be performed simultaneously.
For example, the above step (1) and step (2a) may be performed simultaneously (combined step (A)). As a method for carrying out step (1) and step (2a) simultaneously, for example, high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms are put into a closed container, preferably in the absence of oxygen. and then heating or heating the high molecular weight PTFE and irradiating the high molecular weight PTFE with radiation.

As a specific method for carrying out the composite step (A), high-molecular-weight PTFE and the substance capable of generating free hydrogen atoms are placed in a sealed container, preferably in the absence of oxygen, and then heated. Alternatively, a method of heating or heating the closed container using an external unit having a heating function and irradiating the high molecular weight PTFE with γ-rays, X-rays or electron beams from the outside of the closed container.
As the γ-rays, for example, γ-rays generated from cobalt-60 can be used.
As the X-rays, for example, X-rays generated by irradiating a target with an electron beam from an electron accelerator can be used. Alternatively, quasi-monochromatic X-rays generated by inverse Compton scattering (laser Compton scattering) by colliding laser light with high-energy electron beams from a linear accelerator can be used. Furthermore, X-rays can be generated by synchrotron radiation, or X-rays can be generated by installing an undulator or wiggler in the lower stage of the particle accelerator.
By using γ-rays and X-rays, which are excellent in material penetrating power, the external unit can be arranged at arbitrary positions such as the entire circumference, the outer circumference, the upper and lower parts, the left and right parts, and the front and rear parts of the closed container. From the viewpoint of facilitating transmission of γ-rays and X-rays, it is preferable not to arrange the external unit on the irradiation surface side.
Electron beams, which are inferior to γ-rays and X-rays in material penetrating power, can be used instead of the γ-rays or X-rays. In this case, it is preferable to dispose the external unit on a side other than the side irradiated with the electron beam.
Also, a heating or heating mechanism may be incorporated into the sealed container itself.

In the composite step (A), the heating or heating temperature is more preferably 70° C. or higher, still more preferably 100° C. or higher, and preferably 310° C. or lower.
A method for warming or heating the sample is not particularly limited, but it may be a beam heating method for converting radiation energy into thermal energy. When the beam heating method is used, it is preferable to use, as the radiation, an electron beam from an electron accelerator or an X-ray generated by irradiating a target with an electron beam from the electron accelerator. A heat insulating material or the like may be arranged on the entire periphery of the sealed container, the outer peripheral portion, the upper and lower portions, the left and right portions, the front and rear portions, or the like. From the viewpoint of facilitating transmission of radiation, it is preferable not to place a heat insulating material or the like on the irradiation surface side.

Moreover, the above step (1) and step (2c) may be performed simultaneously (combined step (C)).
However, since free hydrogen atoms generated from the substance capable of generating free hydrogen atoms used in step (1) have radical scavenging ability, in the production method of the present disclosure, composite step (C) is not performed. is also preferred.
As a method for carrying out step (1) and step (2c) at the same time, for example, high molecular weight PTFE and a substance capable of generating free hydrogen atoms are charged into a sealed container, preferably in the absence of oxygen. Then, a method of irradiating the high-molecular-weight PTFE with the gas having the radical-scavenging ability sealed in a sealed container.

As a specific implementation method of the composite step (C), high molecular weight PTFE and a substance capable of generating free hydrogen atoms are charged into a closed container in the substantial absence of oxygen, and then mixed with a concentration of 3% or more. Examples include a method of irradiating the high-molecular-weight PTFE with γ-rays, X-rays or electron beams from the outside of the closed container while enclosing or circulating the gas having the radical-scavenging ability in the closed container.
As the γ-rays, for example, γ-rays generated from cobalt-60 can be used.
As the X-rays, for example, X-rays generated by irradiating a target with an electron beam from an electron accelerator can be used. Alternatively, quasi-monochromatic X-rays generated by inverse Compton scattering (laser Compton scattering) by colliding laser light with high-energy electron beams from a linear accelerator can be used. Furthermore, X-rays can be generated by synchrotron radiation, or X-rays can be generated by installing an undulator or wiggler in the lower stage of the particle accelerator.
By using γ-rays and X-rays, which have excellent material penetrating power, the external unit can be arranged at arbitrary positions such as the entire periphery, outer periphery, top and bottom, left and right, and front and rear of the closed container. From the viewpoint of facilitating transmission of γ-rays and X-rays, it is preferable not to arrange the external unit on the irradiation surface side.
Electron beams, which are inferior to γ-rays and X-rays in material penetrating power, can be used instead of the γ-rays or X-rays. In this case, it is preferable to dispose the external unit on a side other than the side irradiated with the electron beam.
Also, a heating or heating mechanism may be incorporated into the sealed container itself.

Heating or heating may be performed in the composite step (C). The heating or heating temperature is preferably 19° C. or higher, more preferably 30° C. or higher, still more preferably 70° C. or higher, and preferably 310° C. or lower.
A method for warming or heating the sample is not particularly limited, but it may be a beam heating method for converting radiation energy into thermal energy. When the beam heating method is used, it is preferable to use, as the radiation, an electron beam from an electron accelerator or an X-ray generated by irradiating a target with an electron beam from the electron accelerator. A heat insulating material or the like may be arranged on the entire periphery of the sealed container, the outer peripheral portion, the upper and lower portions, the left and right portions, the front and rear portions, or the like. From the viewpoint of facilitating transmission of radiation, it is preferable not to place a heat insulating material or the like on the irradiation surface side.

The present disclosure is a method for producing a low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, wherein the sample temperature during irradiation with radiation is High-molecular-weight polytetrafluoroethylene in the presence of a substance capable of generating free hydrogen atoms under the conditions of fluoroethylene's room temperature transition temperature ( _β1 dispersion temperature) or higher, 320°C or lower, and a dose rate of 0.1 kGy/s or higher. The present invention also relates to a method for producing low-molecular-weight polytetrafluoroethylene, characterized by including the step (X) of obtaining the low-molecular-weight polytetrafluoroethylene by irradiating radiation to the polytetrafluoroethylene.

The above step (X) may be carried out in a space substantially free of oxygen, but may also be carried out in an atmospheric atmosphere containing oxygen. In addition, the component adjustment may be performed in an atmospheric atmosphere. Examples of the component-adjusted atmosphere include atmosphere containing oxygen to which 0.5% by volume or more of hydrogen gas, halogen gas, or the like having radical scavenging ability is added as a single gas or a composite gas.
It is reported in the literature (Radiat. Phys. Chem. Vol. 50, pp. 611-615, 1997) that the decomposition efficiency is improved by irradiating PTFE while it is heated to a temperature below the crystalline melting point of PTFE. .
In this state, even in an atmospheric atmosphere containing 21% by volume of oxygen, a radiation source such as an electron beam with a high dose rate is used to irradiate at elevated temperatures, so that before the generated terminal radicals react with oxygen, The present inventors have found that the main chain scission progresses in , and the decomposition reaction is promoted.
According to conventional academic technical knowledge, when high-molecular-weight PTFE is exposed to radiation in an atmosphere containing oxygen (especially in the air), oxidative degradation occurs, and perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof is formed. expected to be produced in large quantities. Surprisingly, however, as described above, under the conditions where the irradiation temperature is equal to or higher than the _β1 dispersion temperature and the dose rate is extremely limited, and in the presence of substances capable of generating free hydrogen atoms, the atmospheric atmosphere The present inventors have found that perfluorocarboxylic acids having 4 to 14 carbon atoms or salts thereof are less likely to be produced even when irradiation is performed in the atmosphere.

The temperature of _the sample during irradiation in the above step (X) is 19°C or higher, and is ₁₉ °C or higher, and is 30°C or higher. It is preferably 50° C. or higher, still more preferably 70° C. or higher, even more preferably 100° C. or higher, and particularly preferably alpha dispersion temperature or higher (130° C. or higher). The sample temperature during the irradiation is also below 320°C.
The temperature at the time of irradiation in the above step (X) is determined by measuring the temperature of the atmosphere in which the process is performed with a thermocouple, platinum resistor, etc., or by measuring the temperature of the sample surface or inside the sample with a thermocouple, platinum resistor, etc. It can be easily measured by a method of measuring with an equation or a method of measuring infrared radiation from the sample surface with an infrared radiation thermometer.
The sample temperature may vary between 19°C and 320°C during the irradiation of step (X).

The radiation in step (X) may be electron beams or X-rays. The electron beam may be an electron beam generated from an electron accelerator. The X-rays may be X-rays generated by irradiating a target with a particle beam from a particle accelerator, and quasi-monochromatic generated by inverse Compton scattering by colliding a laser with a high-energy electron beam from a linear accelerator. It may be a sexual X-ray. Furthermore, X-rays can be generated by synchrotron radiation, or X-rays can be generated by installing an undulator or wiggler in the lower stage of the particle accelerator.

The substance capable of generating a free hydrogen atom in the step (X) includes the same substance as the substance capable of generating a free hydrogen atom that can be used in the step (1), and the amount thereof used is also the same. .

As a specific method for carrying out the step (X), high molecular weight PTFE is placed in a container having a heating or heating mechanism, and while being heated or heated in the atmosphere, electrons are applied to the high molecular weight PTFE from the outside of the container. Examples include a method of irradiating X-rays or X-rays.
As the electron beam, for example, an electron beam generated from an electron accelerator can be used.
As the X-rays, for example, X-rays generated by irradiating a target with an electron beam from an electron accelerator can be used.
In the case of using X-rays, which are excellent in material penetrating power, the heating mechanism can be arranged at arbitrary positions such as the entire circumference, the outer circumference, the upper and lower parts, the left and right parts, and the front and rear parts of the container. From the viewpoint of facilitating transmission of X-rays, it is preferable not to arrange the heating mechanism on the irradiation surface side.
When using electron beams, which are inferior to X-rays in material penetrating power, it is preferable to dispose the heating mechanism on a side other than the side irradiated with the electron beams.

The dose rate in the step (X) is 0.1 kGy/s or more, preferably 1 kGy/s or more, more preferably 10 kGy/s or more. Alternatively, it is preferably 0.1 kGy/pass or more, more preferably 1 kGy/pass or more, and even more preferably 10 kGy/pass or more.

The radiation irradiation in the step (X) may be performed continuously until the desired absorption dose is reached, or may be performed intermittently and repeatedly until the desired absorption dose is reached in total. When it is repeated intermittently, the remaining radicals are oxidized during the intermittent irradiation interval and become peroxide radicals. In order to prevent the formation of carboxylic acid or a salt thereof, the interval time between intermittent irradiations is preferably within 5 minutes, more preferably within 3 minutes, and even more preferably within 1 minute.

The above step (X) can also be carried out in the presence of a substance capable of scavenging radicals. Examples of the substance having radical scavenging ability include substances that can be used in step (2c). As for the amount of the above substances used and the method of introducing them, the amount and method according to the step (2c) can be adopted.
However, since the free hydrogen atoms generated from the substance capable of generating free hydrogen atoms used in step (X) have radical scavenging ability, in step (X), substances other than the above-mentioned substances capable of generating free hydrogen atoms In addition, it is also preferable not to use a substance having radical scavenging ability.

The present disclosure is a method for producing low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380°C of 1.0 × 10 ² to 7.0 × 10 ⁵ Pa·s, wherein the melt viscosity at 380°C is 1.0 Polytetrafluoroethylene of ×10 ² to 7.0×10 ⁵ Pa·s is irradiated with radiation in the presence of a substance capable of generating free hydrogen atoms, thereby reducing the molecular weight of the polytetrafluoroethylene. The step (Y1), and the step of obtaining the low-molecular-weight polytetrafluoroethylene (Y2) by deactivating at least part of the main chain radicals and terminal radicals generated by the irradiation substantially in the absence of oxygen. It also relates to a process for producing low-molecular-weight polytetrafluoroethylene, characterized in that it comprises:
Even when PTFE with a low melt viscosity (low molecular weight) is irradiated with radiation as described above, the formation of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof, particularly perfluorooctanoic acid and salts thereof is suppressed. be able to.

The PTFE irradiated in the above step (Y1) may be obtained by direct polymerization or may be obtained by thermal decomposition of high molecular weight PTFE. It may be obtained by

The substance capable of generating a free hydrogen atom in the step (Y1) includes the same substance as the substance capable of generating a free hydrogen atom that can be used in the step (1), and the amount thereof used is also the same. .

Suitable aspects and conditions of the step (Y1) may be the same as those of the step (1) described above. ) should be adjusted accordingly.
Suitable aspects and conditions of the step (Y2) may be the same as those of the step (2) described above.

In the production method of the present disclosure, before step (1), compounding step (A), compounding step (C), or step (X), the high-molecular-weight PTFE is further heated to a temperature equal to or higher than its primary melting point for molding. A step (3) of obtaining the product may also be included. In this case, the molded article obtained in step (3) can be used as the high molecular weight PTFE in step (1).
The primary melting point is preferably 300° C. or higher, more preferably 310° C. or higher, and even more preferably 320° C. or higher.
The primary melting point means the maximum peak temperature of the endothermic curve appearing on the crystal melting curve when the unsintered high-molecular-weight PTFE is measured with a differential scanning calorimeter. The endothermic curve was obtained by using a differential scanning calorimeter to raise the temperature at a temperature elevation rate of 10° C./min.

The molded product in step (3) preferably has a specific gravity of 1.0 g/cm ³ or more, more preferably 1.5 g/cm ³ or more, and 2.5 g/cm ³ or less. is preferred. When the specific gravity of the molded article is within the above range, pores and unevenness on the surface are reduced, and as a result, low-molecular-weight PTFE with a small specific surface area can be obtained.
The above specific gravity can be measured by a water substitution method.
The production method of the present disclosure may further include, after step (3), the step of pulverizing the molded article to obtain the high-molecular-weight PTFE powder. The molded article may be coarsely pulverized and then further pulverized into small pieces.

In the production method of the present disclosure, after step (2), compounding step (A), compounding step (C), step (X), or step (Y2), the low-molecular-weight PTFE is further pulverized to obtain low-molecular-weight PTFE can also include the step of obtaining a powder of Even if the low-molecular-weight PTFE obtained by the production method of the present disclosure is pulverized, the content of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof does not increase.

The method of pulverization is not particularly limited, but a method of pulverizing with a pulverizer can be mentioned. The pulverizer includes an impact type such as a planetary mill, a hammer mill, a pin mill, and a jet mill, and a grinding type such as a cutter mill that pulverizes by shearing force caused by unevenness of a rotating blade and an outer peripheral stator.

The pulverization temperature is preferably -200°C or higher and lower than 50°C. In freezing pulverization, the temperature is usually -200 to -100°C, but pulverization may be performed at a temperature around room temperature (10 to 30°C). Frozen pulverization generally uses liquid nitrogen, but requires a large amount of equipment and high pulverization costs. Pulverization at 10°C or higher and less than 50°C is more preferable, pulverization at 10 to 40°C is even more preferable, and pulverization at 10 to 30°C is more preferable in terms of simplifying the process and reducing pulverization cost. is particularly preferred.

After the pulverization, fine particles and fibrous particles may be removed by air classification, and then coarse particles may be further removed by classification.

In the air classification, pulverized particles are sent to a columnar classification chamber by decompressed air, dispersed by a swirling air current in the chamber, and fine particles are classified by centrifugal force. Fines are collected from the center into cyclones and bag filters. Rotating bodies such as conical cones and rotors are installed in the classifying chamber so that the pulverized particles and air can be uniformly swirled.

When a classifying cone is used, the classification point is adjusted by adjusting the volume of secondary air and the gap between the classifying cones. When a rotor is used, the air volume in the classifying chamber is adjusted by the rotation speed of the rotor.

Methods for removing coarse particles include airflow classification using a mesh, vibrating sieves, ultrasonic sieves, etc. Airflow classification is preferred.

In the production method of the present disclosure, the low-molecular-weight PTFE obtained in step (2), compounding step (A), compounding step (C), step (X), or step (Y2) is further exposed to UV rays, particularly from the natural environment. It may include a step (4) of storing in an environment shielded from ultraviolet rays from fluorescent lamps.
When the low-molecular-weight PTFE obtained in the step (2), the compounding step (A), the compounding step (C), the step (X), or the step (Y2) is exposed to the air, a slight remaining main chain radical and/or Peroxides derived from terminal radicals may occur. When this peroxide is exposed to ultraviolet rays, the main chain radical and/or the terminal radical may be regenerated. Or there is a possibility that its salt is generated.
By carrying out the step (4), generation of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof can be suppressed for a long period of time.

The ultraviolet rays shielded in step (4) may be ultraviolet rays with a wavelength of 450 nm or less, including visible light. Ultraviolet rays with a wavelength of 400 nm or less are preferable, and ultraviolet rays with a wavelength of 385 nm or less are more preferable. The lower limit of the wavelength of the ultraviolet rays is preferably 200 nm.

The storage in step (4) is, for example, holding the low-molecular-weight PTFE in a container capable of shielding the ultraviolet rays, or shielding the container holding the low-molecular-weight PTFE from the ultraviolet rays. can be carried out by holding it in a space (such as a warehouse) where

The temperature of the storage environment in step (4) is preferably equal to or lower than the α-dispersion temperature of uncrosslinked PTFE, more preferably -273 to 130°C, and even more preferably -196 to 130°C. -80 to 70°C is even more preferred. By setting the temperature within the above range, generation of perfluorocarboxylic acid having 4 to 14 carbon atoms or a salt thereof during storage can be further suppressed.

In the production method of the present disclosure, the product obtained after performing the step (2), the composite step (A), the composite step (C), the step (X), or the step (Y2) contains the low-molecular-weight PTFE together with the free Contains substances that can generate hydrogen atoms. The substance in the product is at least partially decomposed or crosslinked.
The above product may be used as it is, or may be used after removing the remaining substances capable of generating the free hydrogen atoms. The removal method is not particularly limited, and a known method can be adopted according to the form of the substance capable of generating the free hydrogen atom.
The removed substance capable of generating free hydrogen atoms can be used again in step (1).

Next, high molecular weight PTFE irradiated in step (1), composite step (A), composite step (C) or step (X) of the production method of the present disclosure, and step (2), composite step (A ), the low-molecular-weight PTFE obtained after carrying out the compounding step (C) or step (X).
In addition, PTFE irradiated in step (Y1) and low-molecular-weight PTFE obtained after step (Y2) are also described.

The low-molecular-weight PTFE obtained after performing the step (2), the composite step (A), the composite step (C), or the step (X) has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10. ⁵ Pa·s. In the present disclosure, "low molecular weight" means that the above melt viscosity is within the above range.
The melt viscosity is preferably 1.0×10 ³ Pa·s or more, more preferably 1.5×10 ³ Pa·s or more, and 3.0×10 ⁵ Pa·s or less. and more preferably 1.0×10 ⁵ Pa·s or less.

The low-molecular-weight PTFE obtained after performing step (Y2) has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s. The melt viscosity is preferably 3.0×10 ⁵ Pa·s or less, more preferably 1.0×10 ⁵ Pa·s or less.

The PTFE irradiated in step (Y1) has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s. The melt viscosity is preferably 5.0 × 10 ² or more, more preferably 1.0 × 10 ³ Pa s or more, and further preferably 1.5 × 10 ³ Pa s or more. preferable.

The above-mentioned melt viscosity is determined according to ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, and a 2g sample preheated at 380°C for 5 minutes under a load of 0.7MPa. It is a value measured while maintaining the above temperature.

The high molecular weight PTFE to be irradiated with radiation preferably has a standard specific gravity (SSG) of 2.130 to 2.230. The standard specific gravity (SSG) is a value measured according to ASTM D4895.

The high-molecular-weight PTFE has a much higher melt viscosity than the low-molecular-weight PTFE, and it is difficult to accurately measure the melt viscosity. On the other hand, although the melt viscosity of low-molecular-weight PTFE can be measured, it is difficult to obtain a molded article that can be used for standard specific gravity measurement from low-molecular-weight PTFE, and it is difficult to measure its accurate standard specific gravity. . Therefore, in the present disclosure, standard specific gravity is used as an index of the molecular weight of the high molecular weight PTFE to be irradiated, and melt viscosity is used as an index of the molecular weight of the low molecular weight PTFE. For both the high-molecular-weight PTFE and the low-molecular-weight PTFE, there is no known measuring method capable of directly specifying the molecular weight.

In the high-molecular-weight PTFE, the amount of perfluorooctanoic acid and its salt may be less than 25 mass ppb, may be 20 mass ppb or less, may be 15 mass ppb or less, or may be 10 mass ppb or less. may be present, may be 5 mass ppb or less, or may be less than 5 mass ppb. The lower limit is not particularly limited, and may be an amount below the detection limit.
The amount of perfluorooctanoic acid and its salt can be measured by liquid chromatography.

The low-molecular-weight PTFE preferably has a melting point of 320 to 340°C, more preferably 324 to 336°C.

The above melting point was measured using a differential scanning calorimeter (DSC), and after temperature calibration in advance using indium and lead as standard samples, about 3 mg of low-molecular-weight PTFE was placed in an aluminum pan (crimped container), and 200 ml/ The temperature range from 250 to 380° C. is raised at a rate of 10° C./min under an air current of 10 min.

In the production method of the present disclosure, the shape of the high-molecular-weight PTFE is not particularly limited, and may be powder (fine powder, molding powder, etc.), a molded article of the high-molecular-weight PTFE, or the It may be cutting waste generated when cutting a molded product of high molecular weight PTFE. When the high-molecular-weight PTFE is powder, the low-molecular-weight PTFE powder can be easily obtained.
Further, the high molecular weight PTFE may be crosslinked.

Moreover, the shape of the low-molecular-weight PTFE obtained by the manufacturing method of the present disclosure is not particularly limited, but it is preferably powder.

When the low-molecular-weight PTFE obtained by the production method of the present disclosure is powder, it preferably has a specific surface area of 0.5 to 20 m ² /g.
The low-molecular-weight PTFE powder includes a low specific surface area type with a specific surface area of 0.5 m ² /g or more and less than 7.0 m 2 /g, a specific surface area of 7.0 ^{m 2 /} g or more and 25 m ² /g or less, A type having a high specific surface area, preferably 20 m ² /g or less, is required.
A low-molecular-weight PTFE powder with a low specific surface area has the advantage of being easily dispersed in a matrix material such as paint, but has a large dispersed particle size in the matrix material and is poor in fine dispersion.
The specific surface area of the low-molecular-weight PTFE powder having a low specific surface area is preferably 1.0 m ² /g or more, preferably 5.0 m ² /g or less, and more preferably 3.0 m ² /g or less. As the matrix material, in addition to plastics and inks, paints and the like are preferably used.
Low-molecular-weight PTFE powder of a type with a high specific surface area, for example, when dispersed in a matrix material such as paint, has a small dispersed particle size in the matrix material, and has the effect of modifying the surface, such as improving the texture of the surface of the coating film. However, it may not easily disperse due to the long time required for dispersing it in the matrix material, and the viscosity of the paint or the like may increase.
The specific surface area of the low-molecular-weight PTFE powder having a high specific surface area is preferably 8.0 m ² /g or more, preferably 25 m ² /g or less, and more preferably 20 m ² /g or less. As the matrix material, in addition to oils, greases, and paints, plastics and the like are preferably used.

The above specific surface area is measured using a surface analyzer (trade name: BELSORP-miniII, manufactured by Microtrack Bell Co., Ltd.), using a mixed gas of 30% nitrogen and 70% helium as a carrier gas, and using liquid nitrogen for cooling. , measured by the BET method.

When the low-molecular-weight PTFE obtained by the production method of the present disclosure is powder, the average particle size is preferably 0.5 to 200 μm, more preferably 50 μm or less, even more preferably 25 μm or less, and particularly preferably 10 μm or less. Since the powder has a relatively small average particle size, it is possible to form a coating film having superior surface smoothness, for example, when it is used as an additive for paint.

The average particle size is measured using a laser diffraction particle size distribution analyzer (HELOS & RODOS) manufactured by JEOL Ltd., without using a cascade, at a dispersion pressure of 3.0 bar, and corresponds to 50% of the integrated particle size distribution. equal to the particle size.

In the production method of the present disclosure, perfluorooctanoic acid and a salt thereof are substantially included after performing step (2), combined step (A), combined step (C), step (X), or step (Y2). low-molecular-weight PTFE can be obtained. In the low-molecular-weight PTFE obtained by the production method of the present disclosure, the amount of perfluorooctanoic acid and its salt may be less than 25 mass ppb, preferably 20 mass ppb or less, and preferably 15 mass ppb or less. It is more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, and particularly preferably less than 5 mass ppb. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
The amount of perfluorooctanoic acid and its salt can be measured by liquid chromatography.

Further, according to the production method of the present disclosure, it is also possible to obtain low-molecular-weight PTFE substantially free of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof. In the low-molecular-weight PTFE obtained by the production method of the present disclosure, the total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof may be 50 mass ppb or less, preferably less than 25 mass ppb, and 20 mass ppb. It is more preferably ppb or less, still more preferably 15 ppb or less by mass, even more preferably 10 ppb or less by mass, particularly preferably 5 ppb or less by mass, and less than 5 ppb by mass. is most preferred. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
The total amount of the perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt is the time after performing the step (2), the composite step (A), the composite step (C), the step (X) or the step (Y2). Therefore, it is preferably within the above range, and more preferably within the above range even after further heating (for example, heating during processing).
The amount of perfluorocarboxylic acid and its salt can be measured by liquid chromatography.
Further, according to the production method of the present disclosure, low-molecular-weight PTFE in which the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof is within the above range can also be obtained.

According to the production method of the present disclosure, perfluorooctanoic acid and its salts, and further the above perfluorocarboxylic acid and its salts, are less likely to be generated by heating during processing such as adding to the matrix resin and heat-molding, and are reliable. It is also possible to produce low molecular weight PTFE with high toughness.
Although the reason is not clear, it is presumed as follows. Upon irradiation with radiation, the free hydrogen atoms generated from the substance capable of generating the free hydrogen atoms are added to the main chain radicals and terminal radicals generated by the irradiation of the high-molecular-weight PTFE. It is thought that the main chain radicals and terminal radicals are sufficiently extinguished by the reaction of the hydrogen molecules generated from the substance capable of generating atoms with the main chain radicals and the terminal radicals. For this reason, even if it is heated in the presence of oxygen at the stage of application, it is possible to prevent the above-mentioned main chain radicals and terminal radicals from reacting with oxygen. It is believed that the formation of salts, particularly perfluorooctanoic acid and salts thereof, can be suppressed.

In the low-molecular-weight PTFE obtained by the production method of the present disclosure, the amount of perfluorooctanoic acid and its salts determined according to the following heating/measurement condition A may be less than 100 mass ppb, or less than 50 mass ppb. , may be less than 25 mass ppb, preferably 20 mass ppb or less, more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, and 5 mass ppb or less is even more preferred, and less than 5 mass ppb is particularly preferred. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
Low-molecular-weight PTFE having the amount of perfluorooctanoic acid and its salts determined according to the heating/measurement condition A within the above range, even when heated in the presence of oxygen at the stage of application to various uses, such as during processing. , less likely to produce perfluorooctanoic acid and its salts.
(Heating/measurement condition A)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
The content of perfluorooctanoic acid and its salts is measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile is added to 1 g of the heated sample, and ultrasonic treatment is performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase is measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous ammonium acetate solution (20 mmol/L) (B) are fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) is used, the column temperature is 40° C., and the injection volume is 5 μL. ESI (Electrospray ionization) Negative is used as the ionization method, the cone voltage is set to 25 V, and precursor ion molecular weight/product ion molecular weight is measured to be 413/369. The content of perfluorooctanoic acid and its salts is calculated using the external standard method.
The detection limit in this measurement is 5 mass ppb.

In the low-molecular-weight PTFE obtained by the production method of the present disclosure, the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof determined according to the heating and measurement conditions B below may be less than 100 mass ppb, and may be 50 mass ppb. It may be less than 25 mass ppb, preferably less than 20 mass ppb, more preferably 20 mass ppb or less, even more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less. , 5 mass ppb or less, and most preferably less than 5 mass ppb. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
Low-molecular-weight PTFE whose amount of perfluorocarboxylic acid and its salt determined according to the heating/measurement condition B is within the above range is heated in the presence of oxygen at the stage of application to various uses, such as during processing. Also, it is difficult to produce the perfluorocarboxylic acid and its salt.
(Heating/measurement condition B)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
Using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD), the content of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof is measured. Using 1 g of the heated sample, a liquid phase obtained by extracting perfluorooctanoic acid and its salt in the same manner as in heating/measurement condition A is used, and measurement is performed using the MRM method. As for the measurement conditions, the concentration gradient was changed from the measurement conditions for perfluorooctanoic acid (A/B = 10/90-1.5 min-90/10-3.5 min), and the precursor ion molecular weight/product ion molecular weight was Nonanoic acid (9 carbon atoms) is 463/419, perfluorodecanoic acid (10 carbon atoms) is 513/469, perfluoroundecanoic acid (11 carbon atoms) is 563/519, perfluorododecanoic acid (12 carbon atoms) is 613/569, 663/619 for perfluorotridecanoic acid (13 carbon atoms), and 713/669 for perfluorotetradecanoic acid (14 carbon atoms).
The total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof was calculated using the following formula from the perfluorooctanoic acid content (X) obtained from the above measurement. The detection limit in this measurement is 5 mass ppb.
(A _C9 +A _C10 +A _C11 +A _C12 +A _C13 +A _C14 )/A _C8 ×X
A _C8 : Perfluorooctanoic acid peak area A _C9 : Perfluorononanoic acid peak area A _C10 : Perfluorodecanoic acid peak area A _C11 : Perfluoroundecanoic acid peak area A _C12 : Perfluorododecanoic acid peak area A _C13 : Peak area of perfluorotridecanoic acid A _C14 : Peak area of perfluorotetradecanoic acid X: Content of perfluorooctanoic acid calculated using an external standard method from the measurement results using the MRM method

The low-molecular-weight PTFE obtained after performing the step (2), the compounding step (A), the compounding step (C), the step (X), or the step (Y2) has an oxygen atom in a part of the side chain on the main chain or low-molecular-weight PTFE consisting of carbon atoms and fluorine atoms.
The low-molecular-weight PTFE having oxygen atoms in some of the side chains on the main chain, or the low-molecular-weight PTFE consisting of carbon atoms and fluorine atoms has a carbon-carbon bond and has an oxygen atom at the end of the molecular chain. It is a compound that does not contain Its molecular structure shows the structure below.
(Main chain radical/end radical deactivation treatment process)
R ₁ (—CF ₂ —CF ₂ —) _x —R ₂
R ₁ (-CF=CF ₂ -CF ₂ ) _x -R ₂
R ₁ (-CF ₂ -CF(R ₃ )-CF ₂ ) _y -R ₂
R ₁ (-CF=C(R ₄ )-CF ₂ ) _y -R ₂
(Deactivation treatment process for terminal radicals only)
R ₁ (-CF ₂ -CF(R ₅ )-CF ₂ ) _y -R ₂
R ₁ (-CF=C(R ₆ )-CF ₂ ) _y -R ₂
In the above formula, each occurrence of R ₁ is independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a -CF ₃ group, a -CF=CF ₂ group, a -CF=CHF group, a - CH ₂ F group, —CHF ₂ group, or —CH ₃ group.
In the above formula, each occurrence of R ₂ is independently a hydrogen atom, fluorine atom, chlorine atom, bromine atom, iodine atom, —CF ₃ group, —CF=CF ₂ group, —CF=CHF group, — CH ₂ F group, —CHF ₂ group, or —CH ₃ group.
In the above formula, each occurrence of R ₃ is independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a -CF ₃ group, a -CF ₂ -CF ₃ group, a -CF=CF ₂ group. , —CF ₂ CF ₂ — group, or —OR _f group (R _f is a perfluoroorganic group, preferably a perfluoroalkyl group having 1 to 10 carbon atoms).
In the above formula, each occurrence of R ₄ is independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a -CF ₃ group, a -CF ₂ -CF ₃ group, a -CF=CF ₂ group. , —CF ₂ CF ₂ — group, or —OR _f group (R _f is a perfluoroorganic group, preferably a perfluoroalkyl group having 1 to 10 carbon atoms).
In the above formula, each occurrence of R ₅ is independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a -CF ₃ group, a -CF ₂ -CF ₃ group, a -CF=CF ₂ group. , —CF ₂ CF ₂ — group, —OR _f group (R _f is a perfluoroorganic group, preferably a perfluoroalkyl group having 1 to 10 carbon atoms), —OH group, —OF group, —OCl group , —OBr group, —OI group, —O—CF ₃ group, —O—CF ₂ —CF ₃ group, or —O—O. (peroxide radical).
In the above formula, each occurrence of R ₆ is independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a -CF ₃ group, a -CF ₂ -CF ₃ group, a -CF=CF ₂ group. , —CF ₂ CF ₂ — group, —OR _f group (R _f is a perfluoroorganic group, preferably a perfluoroalkyl group having 1 to 10 carbon atoms), —OH group, —OF group, —OCl group , —OBr group, —OI group, —O—CF ₃ group, or —O—CF ₂ —CF ₃ group.
In the above formula, x is an integer of 1-1000, preferably 2-500.
In the above formula, y is an integer of 1-1000, preferably 2-500.
Identification of the above molecular structure is carried out by measurement using a ¹⁹ F nuclear magnetic resonance spectrometer (NMR), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman), and X-ray photoelectric spectroscopy. (XPS) or other means.

The low-molecular-weight PTFE has a ratio of the intensity of the signal corresponding to the main chain radical obtained by electron spin resonance (ESR) measurement to the intensity of the signal corresponding to the terminal radical (main chain radical/terminal radical) of 10. /1 or more, more preferably 15/1 or more, more preferably 20/1 or more, and even more preferably 30/1 or more.
When the signal corresponding to the main chain radical (double quintet) and the signal corresponding to the terminal radical (triplet) are clearly detected in the ESR measurement in vacuum, the ratio is based on the intensity of those signals. If it cannot be clearly detected in a vacuum, the intensity of the signal corresponding to the main chain type (asymmetric) and terminal type (symmetric) peroxide radicals detected in the ESR measurement performed after the sample is exposed to the atmosphere shall be calculated based on Measurement at liquid nitrogen temperature is particularly effective for separation of peroxide radicals.
In the low-molecular-weight PTFE obtained by the conventional method of irradiating high-molecular-weight PTFE in an air atmosphere (without radical deactivation in step (2)), many terminal radicals remain, so the above ratio is Not within the above range.

The low-molecular-weight PTFE preferably has in its molecule at least one selected from the group consisting of a molecular structure containing hydrogen atoms and a molecular chain containing double bonds.
Examples of the molecular structure containing a hydrogen atom include structures represented by -CHF-, =CHF, -CFH ₂ , -CH ₃ group, -CHF ₂ group, and the like.
Examples of molecular chains containing double bonds include structures such as -CF=CF-, -CF=CF ₂ and -CF=CF-CF ₃ .
It is also preferable to have a molecular structure represented by -CF ₂ CF(CF ₃ )CF ₂ -, -CF(CF ₃ ) ₂ or the like.
By carrying out the irradiation in step (1) in the presence of a substance capable of generating free hydrogen atoms, a molecular structure containing hydrogen atoms and a molecular chain containing double bonds are formed inside the resulting low-molecular-weight PTFE. be.
Further, when a closed container made of a material containing hydrogen atoms is used as the closed container for carrying out the step (1), a radiolytic gas containing hydrogen gas as a main component is generated from the closed container during radiation irradiation. By using the cracked gas as the gas having radical scavenging ability in step (2c), a molecular structure containing hydrogen atoms and a molecular chain containing double bonds are formed inside the obtained low-molecular-weight PTFE.
As the material containing a hydrogen atom, an organic material containing a hydrogen atom is preferable, and rubber materials containing a hydrogen atom such as ethylene-propylene rubber, tetrafluoroethylene-propylene rubber, and polyester elastomer; polyesters such as polyethylene terephthalate (PET). , polyamide (PA), polyethylene (PE), polyamideimide (PAI), thermoplastic polyimide (TPI), polyphenylene sulfide (PPS), polyetherimide (PEI), cyclic polyolefin (COP), polyvinylidene fluoride, ethylene - thermoplastic organic materials containing hydrogen atoms such as tetrafluoroethylene copolymers;
Further, when hydrogen gas is directly used as the gas having radical scavenging ability in carrying out step (2c), a molecular structure containing hydrogen atoms and a molecular chain containing double bonds are formed inside the obtained low-molecular-weight PTFE. be done.

It can be confirmed by ¹⁹ F MAS NMR under any of the following measurement conditions that the low-molecular-weight PTFE has the structure described above in its molecule.
<Measurement conditions (1)>
Apparatus: VNS600 manufactured by Varian
Resonance frequency: 564.491MHz
Observation nucleus: ¹⁹ F
Sample tube diameter: 1.2mmφ
Rotation speed: 50kHz
Measurement temperature: rt (23.3°C)
Measurement method: single pulse method Accumulated times: 512 times or more Waiting time: 5 seconds or more Pulse width: 1.15 μs
<Measurement conditions (2)>
Apparatus: AVANCE III HD400 manufactured by Bruker
Resonance frequency: 376.6412776MHz
Observation nucleus: ¹⁹ F
Sample tube diameter: 1.3mmφ
Rotation speed: 60 kHz
Measurement temperature: 70°C
Measurement method: single pulse method Accumulated times: 10,000 times or more Waiting time: 5 seconds or more Pulse width: 0.8 μs
Confirm the signal attributed to -CHF ₂ around -140 ppm, the signal attributed to =CHF around -150 ppm, and the signal attributed to -CHF- or -CFH ₂ around -210 ppm to -215 ppm. can be done. A signal attributed to -CF=CF- can be confirmed around -156 ppm. Signals attributed to -CF=CF ₂ can be confirmed near -92 ppm and -190 ppm. Signals attributed to -CF=CF-CF ₃ can be confirmed near -75 ppm and -128 ppm. Signals attributed to -CF ₂ CF(CF ₃ )CF ₂ - can be confirmed near -71 ppm and -114 ppm. A signal attributed to -CF(CF ₃ ) ₂ can be confirmed around -58 ppm.
In addition, it can be confirmed by conducting ¹³ C CP/MAS NMR measurement continuously after ¹ H NMR measurement under the following measurement conditions that the low-molecular-weight PTFE has a structure containing hydrogen atoms.
<Measurement conditions (3)>
Apparatus: AVANCEIII600 wide-bore spectrometer manufactured by Bruker
Resonance frequency: Hydrogen 600.23MHz Carbon 150.9MHz
Observation nuclei: ¹ H and ¹³ C
Sample tube diameter: 2.5 mmφ or 4.0 mmφ
Rotation speed: 6 kHz
Measurement temperature: rt (24.1°C)
Decoupling method: CW/TPPM method Time constant: 3.0 ms
Accumulated times: 65,536 times or more From the above measurements, a signal attributed to —CH ₃ can be detected around 17 ppm.

Electron spin resonance (ESR) measurement under vacuum without contacting the low-molecular-weight PTFE obtained by carrying out steps (1) and (2) under vacuum shows that triplet corresponding to terminal radicals and a double quintet peak corresponding to the main chain radical (alkyl radical) are observed.
When the peak height at the center of the triplet is Peak M and the peak height of the double quintet is Peak A, the ratio Peak M/Peak A is preferably less than 3.0 and less than 2.5 is more preferable, and less than 2.0 is even more preferable.
Also, the ratio Peak A/Peak M is preferably greater than 0.3, more preferably greater than 0.4, and even more preferably greater than 0.45.
FIG. 1 shows an example of the above peaks.

The ESR measurement is performed under vacuum under the following conditions.
Apparatus: JES-X330 manufactured by JEOL Ltd. (JEOL)
Measurement temperature: 23±1°C
Microwave frequency: 9.42-9.44GHz
Microwave power: 0.1mW and 0.04mW
Central magnetic field: 337.0mT
Sweep width: ±25mT
Sweep time: 2 minutes Time constant: 0.1 seconds Magnetic field modulation width: 0.2 mT
Number of scans: 1 Modulation frequency: 100 kHz

According to the production method of the present disclosure, low-molecular-weight PTFE having hydrogen atoms in the molecule can be produced. When the high-molecular-weight PTFE is irradiated with ionizing radiation in the absence of substantially oxygen and in the presence of a substance capable of generating free hydrogen atoms, the free hydrogen atoms cap the carbon radicals in the molecules generated by the irradiation. This produces low molecular weight PTFE molecules with hydrogen atoms. Hydrogen atoms in the low-molecular-weight PTFE molecules are detected as functional groups derived from hydrogen adducts at an absorption frequency of around 3000 to 4000 cm ⁻¹ .

According to the production method of the present disclosure, for example, the following low-molecular-weight PTFE can be produced.

Low molecular weight PTFE (1):
A melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s,
The peak obtained by electron spin resonance measurement under vacuum satisfies the following relational expression (I), the content of perfluorooctanoic acid and its salt is less than 25 mass ppb, and the heating and measurement conditions described above Low-molecular-weight polytetrafluoroethylene having a content of perfluorooctanoic acid and salts thereof determined according to A of less than 100 mass ppb.
Relational expression (I): 3.0>Peak M/Peak A>0.3
(In the formula, Peak M represents the peak height at the center of the triplet corresponding to the terminal radical in the low-molecular-weight polytetrafluoroethylene, and Peak A represents the peak height of the double quintet corresponding to the main chain radical in the low-molecular-weight polytetrafluoroethylene. represents the peak height.)

Low-molecular-weight PTFE (1) has a peak obtained by ESR measurement under vacuum that satisfies the above relational expression (I). Satisfying the above relational expression (I) indicates that the amount of alkyl-type peroxide radicals on the main chain and the peroxide radicals trapped at the ends of the molecular chains are almost non-existent.
The conditions for ESR measurement under vacuum are as described above.

In the low-molecular-weight PTFE (1), the ratio Peak M/Peak A is more preferably less than 2.5, even more preferably less than 2.0.
Also, the ratio Peak A/Peak M is more preferably greater than 0.4, and even more preferably greater than 0.45.

Low molecular weight PTFE (1) can be produced by performing all steps without ever exposing the product to oxygen.

Low molecular weight PTFE (2):
The melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, and the peak obtained by electron spin resonance (ESR) measurement in the atmosphere is represented by the following relational expressions (1) and ( 2) is satisfied, the content of perfluorooctanoic acid and its salts is less than 25 mass ppb, and the content of perfluorooctanoic acid and its salts determined according to the above-described heating and measurement conditions A is less than 100 mass ppb low molecular weight polytetrafluoroethylene.
Relational expression (1): Peak M2/Peak A1≧1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak A1 represents the intensity on the main chain of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the negative peak intensity corresponding to the alkyl-type peroxide radical trapped in ).
Relational expression (2): Peak M2/Peak M3<1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak M3 represents the molecular-chain end of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the positive peak intensity corresponding to the peroxide radical trapped in ).

Low-molecular-weight PTFE (2) satisfies the above relational expressions (1) and (2) in terms of peaks obtained by ESR measurement in air. As a result, the amount of alkyl-type peroxide radicals on the main chain is present at a rate of 90.91% or more of the amount of peroxide radicals trapped at the ends of the molecular chains.
The ESR measurement is carried out under the following conditions in the atmosphere.
Device: JES-RE2X manufactured by JEOL Ltd. (JEOL)
Measurement temperature: 24±2°C
Microwave frequency: 9.42-9.44GHz
Microwave power: 0.1mW and 0.04mW
Central magnetic field: 333.0mT
Sweep width: ±15mT or ±25mT
Sweep time: 2 minutes Time constant: 0.1 seconds Magnetic field modulation width: 0.2 mT
Number of scans: 1 Modulation frequency: 100 kHz

In the above ESR measurement (under air), a negative peak M2 corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight PTFE, a positive peak corresponding to the peroxide radical trapped at the molecular-chain end of the low-molecular-weight PTFE A peak M3 and a negative peak A1 corresponding to alkyl-type peroxide radicals trapped on the main chain of low-molecular-weight PTFE are mainly observed.
Peak M2 may be a positive peak observed at magnetic field strengths of 332.0-333.0 mT.
Peak M3 may be a negative peak observed at magnetic field strengths of 333.2-334.2 mT.
Peak A1 may be a negative peak observed at magnetic field strengths of 334.5-335.5 mT.
An example of these peaks is shown in FIG. A peak M1 is a combination of the peaks M2 and M3.
It should be noted that the low-molecular-weight PTFE obtained by irradiation in the presence of oxygen has a smaller peak A1.

In relational expression (1), Peak M2 represents the absolute value of the intensity of peak M2 described above, and Peak A1 represents the absolute value of the intensity of peak A1 described above.
In relational expression (1), Peak M2/Peak A1 is 1.0 or more, preferably 1.2 or more. Peak M2/Peak A1 may also be 6.0 or less, preferably 5.5 or less.

In relational expression (2), Peak M2 represents the absolute value of the intensity of peak M2 described above, and Peak M3 represents the absolute value of the intensity of peak M3 described above.
In relational expression (2), Peak M2/Peak M3 is less than 1.0, preferably 0.9 or less. Peak M2/Peak M3 may also be 0.1 or more, preferably 0.2 or more.

It is also preferred that the low molecular weight PTFE (2) is a TFE homopolymer.

Low molecular weight PTFE (3):
It has a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C. and is selected from the group consisting of =CHF, —CHF—, —CH ₂ F, —CHF ₂ and —CH ₃ . at least one selected from the group consisting of a molecular structure containing at least one hydrogen atom, CF ₃ - at the molecular chain end, and -CF=CF-, -CF=CF ₂ and -CF=CF-CF ₃ The content of perfluorooctanoic acid and its salts is less than 25 ppb by mass, and the content of perfluorooctanoic acid and its salts is determined according to the heating and measurement conditions A described above. Low molecular weight polytetrafluoroethylene having a content of less than 100 mass ppb.

Low-molecular-weight PTFE (3) has a molecular structure containing at least one hydrogen atom selected from the group consisting of -CHF-, =CHF, _-CH2F , _-CHF2 and _-CH3 , and CF ₃ — and molecular structures containing at least one double bond selected from the group consisting of —CF=CF—, —CF=CF ₂ and —CF=CF-CF ₃ . As a result, the low-molecular-weight PTFE (3) has excellent compatibility with different types of organic substances containing hydrogen atoms.
Low-molecular-weight PTFE (3) has a molecular structure containing at least one hydrogen atom selected from the group consisting of —CHF—, ═CHF, —CH ₂ F, and —CHF ₂ , and CF ₃ — at the end of the molecular chain. , -CF=CF- _CF3 , and -CHF-, =CHF, _-CH2F and _-CHF2 , and _CF3 at the end of the molecular chain. - and a molecular structure represented by -CF=CF-CF ₃ is more preferred.
It can be confirmed by ¹⁹ F MAS NMR that the low-molecular-weight PTFE has the structure described above in its molecule. The measurement conditions and the position of the signal attributed to each structure are as described above.

Low molecular weight PTFE (4):
It has a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C. and is selected from the group consisting of —CF ₂ CF(CF ₃ )CF ₂ — and —CF(CF ₃ ) ₂ at least one molecular structure selected from the group consisting of CF ₃ - at the molecular chain end, -CF=CF-, -CF=CF ₂ and -CF=CF-CF ₃ and a molecular structure containing a bond, the content of perfluorooctanoic acid and its salts is less than 25 ppb by mass, and the content of perfluorooctanoic acid and its salts determined according to the above-described heating and measurement conditions A is 100 Low molecular weight polytetrafluoroethylene that is less than ppb by weight.

Low-molecular-weight PTFE (4) has at least one molecular structure selected from the group consisting of —CF ₂ CF(CF ₃ )CF ₂ — and —CF(CF ₃ ) ₂ , and CF ₃ — at the end of the molecular chain. , -CF=CF-, -CF= _CF2 and -CF=CF- _CF3 .
Low-molecular-weight PTFE (4) has a molecular structure represented by CF ₂ CF(CF ₃ )CF ₂ — and —CF(CF ₃ ) ₂ , CF ₃ — at the end of the molecular chain, and —CF=CF—, — and the molecular structures represented by CF= _CF2 and -CF=CF- _CF3 .
Low-molecular-weight PTFE (4) has a molecular structure represented by —CF ₂ CF(CF ₃ )CF ₂ —, a molecular chain terminal CF ₃ —, and a molecular structure represented by —CF=CF—CF ₃ . It is also preferred to include
It can be confirmed by ¹⁹ F MAS NMR that the low-molecular-weight PTFE has the structure described above in its molecule. The measurement conditions and the position of the signal attributed to each structure are as described above.

Low molecular weight PTFE (5):
The melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, the standard value obtained by the following formula (3) is 1.1 to 10.0, and perfluorooctanoic acid and low-molecular-weight polytetrafluoroethylene having a salt content of less than 25 mass ppb.
Formula (3):
Standard value = (absorbance of the functional group derived from the hydrogenated product of the low-molecular-weight PTFE) / (hydrogenation of the low-molecular-weight PTFE obtained by irradiation in the absence of a substance capable of generating free hydrogen atoms) absorbance of functional groups derived from the body)

Absorbance corresponding to the functional group derived from the hydrogen adduct can be measured by the following method.
(Measuring method)
It conforms to the terminal group analysis method described in JP-A-4-20507.
A low-molecular-weight PTFE powder is preformed by a hand press to produce a film with a thickness of 0.1 to 1.0 mm. Infrared absorption spectrum analysis is performed on the produced film. Infrared absorption spectrum analysis was also performed on PTFE, which was prepared by contacting PTFE with fluorine gas and the functional groups present in the molecule were completely removed by fluorination. Absorbance heights corresponding to groups can be measured.
The obtained difference spectrum is expanded in the range of 3000 cm ⁻¹ to 4000 cm ⁻¹ and baselined in the range of 3300 cm ⁻¹ to 3970 cm ⁻¹ . At that time, by measuring the height of the peak top at 3556 cm ⁻¹ , the absolute value of the absorbance corresponding to the functional group derived from the hydrogen adduct in the PTFE molecule can be obtained.

The standard value is 1.1 to 10.0, preferably 1.1 to 8.0, more preferably 1.1 to 6.0.

The fact that the standard value is within the above range indicates that the low-molecular-weight PTFE was obtained by irradiation in the presence of a substance capable of generating free hydrogen atoms.

The low-molecular-weight PTFE obtained by irradiation in the absence of the substance capable of generating free hydrogen atoms in formula (3) is irradiated in the absence of the substance capable of generating free hydrogen atoms. It is preferably produced under the same conditions as the low-molecular-weight PTFE (5), except for one point.

In addition, when ionizing radiation is irradiated in the absence of a substance that can generate free hydrogen atoms, theoretically, the absorbance corresponding to the functional group derived from the hydrogen adduct in the PTFE molecule is 0.000. . However, in practice, the absorbance is usually 0.001 to 0.005 due to a very small amount of free hydrogen atoms generated from a container or the like used in the ionizing radiation irradiation step.

Suitable melt viscosities of low-molecular-weight PTFE (1) to (5), content of perfluorooctanoic acid and salts thereof, content of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof, and 9 to 9 carbon atoms The contents of 14 perfluorocarboxylic acids and salts thereof are the same as those described above for the low-molecular-weight PTFE obtained by the production method of the present disclosure.

Low-molecular-weight PTFE (1) to (5) not only contain extremely small amounts of perfluorocarboxylic acids including perfluorooctanoic acid and their salts, but also can be used in the presence of oxygen during processing and other stages of application to various uses. perfluorocarboxylic acids including perfluorooctanoic acid and their salts are less likely to form even when heated to . Low-molecular-weight PTFE (1) to (5) have excellent physical properties that are not inferior to conventionally-known low-molecular-weight PTFE, and can be used in the same manner as conventionally-known low-molecular-weight PTFE, and can be used for the same purposes. can be used.

The low-molecular-weight PTFE preferably has 5 or less carboxyl groups per 10 ⁶ main chain carbon atoms at the ends of the molecular chain. The carboxyl group is more preferably 4 or less, still more preferably 3 or less, per 10 ⁶ carbon atoms in the main chain. The lower limit is not particularly limited, and may be an amount below the detection limit. The carboxyl groups are generated at the molecular chain ends of the low-molecular-weight PTFE, for example, by irradiating the high-molecular-weight PTFE with the radiation in the presence of oxygen.
The above number of carboxyl groups is a value measured by the following method. The detection limit by this measurement method is 0.5.
(Measuring method)
The following measurements are performed according to the terminal group analysis method described in JP-A-4-20507.
A low-molecular-weight PTFE powder is preformed by a hand press to produce a film with a thickness of 0.1 to 1.0 mm. Infrared absorption spectrum analysis is performed on the produced film. Infrared absorption spectrum analysis is also performed on PTFE whose ends are completely fluorinated by contacting PTFE with fluorine gas, and the number of terminal carboxyl groups is calculated by the following equation from the difference spectrum between the two.
Number of terminal carboxyl groups (per 10 ⁶ carbon atoms) = (l x K)/t
l: Absorbance K: Correction coefficient t: Film thickness (mm)
The absorption frequency of the carboxyl group is around 3560 cm ⁻¹ and the correction factor is 440.

The low-molecular-weight PTFE also has a reduced content of functional groups other than carboxyl groups that can be generated by irradiation with radiation in the presence of oxygen or by reaction of radicals generated by irradiation with oxygen. Functional groups other than the carboxyl group include, for example, an acid fluoride group (--COF) at the end of the molecular chain and a carbonyl group (--CO--) in the molecular chain.
The low-molecular-weight PTFE preferably has an absorbance of 0.025 or less, more preferably 0.020 or less, corresponding to the acid fluoride groups at the ends of the molecular chains. The lower limit is not particularly limited, and may be a value below the detection limit.
Also, the absorbance corresponding to the carbonyl group in the molecular chain is preferably 0.020 or less, more preferably 0.010 or less. The lower limit is not particularly limited, and may be a value below the detection limit.
The above absorbance is a value measured according to the terminal group analysis method described in JP-A-4-20507.
The absorption frequency of the acid fluoride group is around 1880 cm ⁻¹ and the absorption frequency of the carbonyl group is around 1810 cm ⁻¹ .

An unstable terminal group derived from the chemical structure of the polymerization initiator or chain transfer agent used in the polymerization reaction of the high-molecular-weight PTFE may occur at the molecular chain end of the low-molecular-weight PTFE. The unstable terminal group is not particularly limited, and examples thereof include -CH ₂ OH, -COOH, -COOCH ₃ and the like.

The low-molecular-weight PTFE may have stabilized unstable terminal groups. The method for stabilizing the unstable terminal group is not particularly limited, and includes, for example, a method of exposing the terminal to a fluorine-containing gas to convert the terminal to a trifluoromethyl group [--CF ₃ ].

The low-molecular-weight PTFE may also be terminally amidated. The terminal amidation method is not particularly limited. A method of contacting with ammonia gas and the like can be mentioned.

When the above-mentioned low-molecular-weight PTFE has stabilized unstable terminal groups or amidated terminals, it is used as an additive to a mating material such as paints, greases, cosmetics, plating solutions, toners, plastics, etc. In addition, it is easy to match with the mating material and can improve dispersibility.

The PTFE to be irradiated may be homo-PTFE consisting only of tetrafluoroethylene (TFE) units, or modified PTFE containing modified monomer units based on modified monomers copolymerizable with TFE units and TFE. good. In the manufacturing method of the present disclosure, the composition of the polymer does not change, so the low-molecular-weight PTFE has the same composition as the irradiated PTFE.

In the modified PTFE, the content of the modified monomer units is preferably 0.001 to 1% by mass, more preferably 0.01% by mass or more, and 0.5% by mass of the total monomer units. The following are more preferable, and 0.1% by mass or less is even more preferable. As used herein, the modified monomer unit means a portion of the molecular structure of the modified PTFE and is derived from the modified monomer, and the total monomer unit refers to all monomers in the molecular structure of the modified PTFE. means a part derived from the body. The content of modified monomer units can be determined by a known method such as Fourier transform infrared spectroscopy (FT-IR).

The modified monomer is not particularly limited as long as it can be copolymerized with TFE. Examples include perfluoroolefins such as hexafluoropropylene [HFP]; chlorofluoroolefins such as chlorotrifluoroethylene [CTFE]; Hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perfluorovinyl ether; perfluoroalkylethylene; ethylene and the like. Moreover, one type of modifying monomer may be used, or a plurality of types thereof may be used.

The perfluorovinyl ether is not particularly limited, and for example, the following general formula (1)
CF ₂ = CF-ORf (1)
(wherein Rf represents a perfluoroorganic group), and the like. As used herein, the above-mentioned "perfluoro organic group" means an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoro organic group may have an ether oxygen.

Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE] in which Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms in the general formula (1). The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

Examples of the perfluoroalkyl group in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Purpleolo(propyl vinyl ether) [PPVE], in which the group is a perfluoropropyl group, is preferred.

As the perfluorovinyl ether, further, in the general formula (1), Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is the following formula:

(Wherein, m represents an integer of 0 or 1 to 4), and Rf is the following formula:

(wherein n represents an integer of 1 to 4).

Perfluoroalkylethylene is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE), (perfluorohexyl)ethylene, (perfluorooctyl)ethylene and the like.

The modified monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PPVE, PFBE and ethylene. More preferably, it is at least one selected from the group consisting of HFP and CTFE.

The above-mentioned low-molecular-weight PTFE is suitably used as molding materials, inks, cosmetics, paints, greases, members for office automation equipment, additives for modifying toner, organic photoreceptor materials for copiers, additives for plating solutions, and the like. can do. Examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide. The low-molecular-weight PTFE is particularly suitable as a thickening agent for grease.

The above low-molecular-weight PTFE is used as an additive for molding materials, for example, to improve the non-stickiness and sliding properties of copy rolls, and to improve the texture of engineering plastic moldings such as furniture surface sheets, automobile dashboards, and home appliance covers. applications, light load bearings, gears, cams, push-phone buttons, projectors, camera parts, applications for improving the lubricity and wear resistance of machine parts that generate mechanical friction such as sliding materials, engineering plastic processing It can be suitably used as an auxiliary agent or the like.

The low-molecular-weight PTFE can be used as an additive for paints to improve the lubricity of varnishes and paints. The low-molecular-weight PTFE can be used as an additive for cosmetics for the purpose of improving the smoothness of cosmetics such as foundation.

The low-molecular-weight PTFE is also suitable for use in improving the oil repellency or water repellency of wax or the like, and in use for improving the slipperiness of grease or toner.

The low-molecular-weight PTFE can also be used as an electrode binder for secondary batteries and fuel cells, a hardness modifier for electrode binders, a water-repellent agent for electrode surfaces, and the like.

Grease can also be prepared using the low molecular weight PTFE and lubricating oil. Since the grease is characterized by containing the low-molecular-weight PTFE and lubricating oil, the low-molecular-weight PTFE is uniformly and stably dispersed in the lubricating oil. Excellent properties such as hygroscopicity.

The lubricating oil (base oil) may be mineral oil or synthetic oil. Examples of the lubricating oil (base oil) include paraffinic and naphthenic mineral oils, synthetic hydrocarbon oils, ester oils, fluorine oils, and synthetic oils such as silicone oils. From the viewpoint of heat resistance, fluorine oil is preferable, and examples of the fluorine oil include perfluoropolyether oil, low polymer of trifluoroethylene chloride, and the like. The low polymer of ethylene trifluorochloride may have a weight average molecular weight of 500-1200.

The grease may further contain a thickening agent. Examples of the thickening agent include metal soap, composite metal soap, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds. Examples of the metallic soap include sodium soap, calcium soap, aluminum soap, lithium soap and the like. Examples of the urea compounds, urea-urethane compounds and urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurethane compounds and mixtures thereof.

The grease preferably contains 0.1 to 60% by mass of the low-molecular-weight PTFE, more preferably 0.5% by mass or more, even more preferably 5% by mass or more, and 50% by mass or less. more preferred. If the amount of low-molecular-weight PTFE is too large, the grease may become too hard and may not exhibit sufficient lubricating properties.

The grease may also contain solid lubricants, extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, viscosity index improvers, detergent dispersants and the like.

The present disclosure includes low-molecular-weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s and a substance capable of generating free hydrogen atoms. It also relates to compositions in which the content of octanoic acid and its salts is less than 25 ppb by weight.
The composition of the present disclosure is a novel low molecular weight PTFE composition having a low content of perfluorooctanoic acid and its salts.

The monomer composition and suitable melt viscosity of the low-molecular-weight PTFE in the composition of the present disclosure are the same as those described above for the low-molecular-weight PTFE obtained by the production method of the present disclosure.

The low-molecular-weight PTFE in the composition of the present disclosure may have in its molecule at least one selected from the group consisting of a molecular structure containing hydrogen atoms and a molecular chain containing double bonds. The molecular structure containing hydrogen atoms and the molecular chain containing double bonds are as described above.

The low-molecular-weight PTFE in the composition of the present disclosure also has the same ESR (under vacuum or atmospheric) peak, molecular structure, and standard value as the low-molecular-weight PTFE (1) to (5) described above. good too. These peaks, molecular structures, and standard values are as described above.

Examples of the substance capable of generating free hydrogen atoms in the composition of the present disclosure include the same substances capable of generating free hydrogen atoms that can be used in step (1) of the production method of the present disclosure. can be done.

The substance capable of generating free hydrogen atoms in the composition of the present disclosure may be at least partially decomposed or crosslinked, or at least partially decomposed or crosslinked by radiation.

The form of the substance capable of generating the free hydrogen atoms in the composition of the present disclosure is not limited.

The content of the substance capable of generating free hydrogen atoms in the composition of the present disclosure is preferably 0.0001 to 1000% by mass, more preferably 1% by mass or more, relative to the low-molecular-weight PTFE. , more preferably 2% by mass or more, particularly preferably 10% by mass or more, more preferably 150% by mass or less, further preferably 100% by mass or less, and 50% by mass or less, and particularly preferably 25% by mass or less.

In the composition of the present disclosure, when the substance capable of generating free hydrogen atoms is a polymer compound (molecular weight of 1000 or more), the amount thereof is 0.1 to 1000% by mass relative to the low molecular weight PTFE. is preferably 1% by mass or more, more preferably 5% by mass or more, particularly preferably 10% by mass or more, and more preferably 100% by mass or less, 50 It is more preferably not more than 25% by mass, and particularly preferably not more than 25% by mass.

In the composition of the present disclosure, when the substance capable of generating free hydrogen atoms is a low-molecular-weight compound (molecular weight less than 1000), the amount thereof is 0.0001 to 100% by mass relative to the low-molecular-weight PTFE. is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and 100% by mass or less is more preferably 50% by mass or less, and particularly preferably 10% by mass or less.

The composition of the present disclosure contains less than 25 mass ppb of perfluorooctanoic acid and its salts. The content of perfluorooctanoic acid and its salt is preferably 20 mass ppb or less, more preferably 15 mass ppb or less, still more preferably 10 mass ppb or less, and 5 mass ppb or less. is even more preferred, and less than 5 mass ppb is particularly preferred. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
The amount of perfluorooctanoic acid and its salt can be measured by liquid chromatography.

In the composition of the present disclosure, the total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof may be 50 mass ppb or less, preferably less than 25 mass ppb, and may be 20 mass ppb or less. It is more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, particularly preferably 5 mass ppb or less, and most preferably less than 5 mass ppb. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
When the composition of the present disclosure is obtained through the above-described step (2), composite step (A), composite step (C), step (X), or step (Y2), the carbon number of 4 to The total amount of 14 perfluorocarboxylic acids and salts thereof is within the above range at the time after performing step (2), composite step (A), composite step (C), step (X) or step (Y2) and more preferably within the above range even after further heating (for example, heating during processing).
The amount of perfluorocarboxylic acid and its salt can be measured by liquid chromatography.
Also, in the composition of the present disclosure, the total amount of perfluorocarboxylic acid having 9 to 14 carbon atoms and its salt is preferably within the above range.

In the composition of the present disclosure, the amount of perfluorooctanoic acid and its salt determined according to the heating and measurement conditions A described above may be less than 100 mass ppb, may be less than 50 mass ppb, or may be less than 25 mass ppb. It is preferably 20 mass ppb or less, more preferably 15 mass ppb or less, still more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, and 5 mass ppb or less. Less than ppb is particularly preferred. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
Compositions in which the amount of perfluorooctanoic acid and its salts determined according to the heating/measurement condition A is within the above range, even when heated in the presence of oxygen at the stage of application to various uses such as during processing, Less likely to produce perfluorooctanoic acid and its salts.

In the composition of the present disclosure, the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof determined according to the heating and measurement conditions B described above may be less than 100 mass ppb, and may be less than 50 mass ppb. , preferably less than 25 mass ppb, more preferably 20 mass ppb or less, even more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, and 5 mass ppb or less. is particularly preferred, most preferably less than 5 mass ppb. The lower limit is not particularly limited, and may be, for example, an amount below the detection limit, 0.001 mass ppb, or 1 mass ppb.
A composition in which the amount of the perfluorocarboxylic acid and its salt obtained according to the heating/measurement condition B is within the above range, even when heated in the presence of oxygen at the stage of applying to various uses such as processing. , less likely to produce the above perfluorocarboxylic acid and its salt.

The composition of the present disclosure can be produced, for example, by the production method of the present disclosure described above.

The composition of the present disclosure can be applied to the same uses as the low-molecular-weight PTFE obtained by the production method of the present disclosure described above. Among others, it can be suitably applied as an additive for molding materials. In particular, when the molding material is the same kind of substance as the substance capable of generating free hydrogen atoms, the composition of the present disclosure can be added as it is, which is preferable.
If necessary, the composition of the present disclosure may be used after removing the above substances capable of generating free hydrogen atoms.
The low-molecular-weight PTFE contained in the composition of the present disclosure has excellent physical properties that are not inferior to conventionally-known low-molecular-weight PTFE, and can be used in the same manner as conventionally-known low-molecular-weight PTFE. can be used for

EXAMPLES Next, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited only to these Examples.

Each numerical value in the examples was measured by the following method.

According to melt viscosity ASTM D 1238, a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die were used to heat a 2 g sample in advance at 380 ° C. for 5 minutes at a load of 0.7 MPa. The measurement was performed while maintaining the

Content of perfluorooctanoic acid and its salts (PFOA) The content of perfluorooctanoic acid and its salts was measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile was added to 1 g of the powder to be measured, and ultrasonic treatment was performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase was measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous solution of ammonium acetate (20 mmol/L) (B) were fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) was used, the column temperature was 40° C., and the injection volume was 5 μL. ESI (Electrospray ionization) Negative was used for the ionization method, the cone voltage was set to 25 V, and precursor ion molecular weight/product ion molecular weight was measured to be 413/369. The content of perfluorooctanoic acid and its salt was calculated using an external standard method. The detection limit in this measurement is 5 mass ppb.

After reheating in air, 2 to 20 g of a sample was filled in a cylindrical airtight container made of stainless steel with a PFOA content of 50 cc in air, covered with a lid, and heated at 150° C. for 18 hours.
Using 1 g of the heated sample, the PFOA content was measured in the same manner as described above.

Content of perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt (PFC) Using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD), perfluorocarboxylic acid having 4 to 14 carbon atoms and The salt content was measured. Using 1 g of the measurement powder, a liquid phase obtained by extracting perfluorooctanoic acid and its salt in the same manner as above was used, and measurement was performed using the MRM method. As for the measurement conditions, the concentration gradient was changed from the measurement conditions for perfluorooctanoic acid (A/B = 10/90-1.5 min-90/10-3.5 min), and the precursor ion molecular weight/product ion molecular weight was Butanoic acid (4 carbon atoms) is 213/169, perfluoropentanoic acid (5 carbon atoms) is 263/219, perfluorohexanoic acid (6 carbon atoms) is 313/269, perfluoroheptanoic acid (7 carbon atoms) is 363/319, perfluorooctanoic acid (8 carbon atoms) is 413/369, perfluorononanoic acid (9 carbon atoms) is 463/419, perfluorodecanoic acid (10 carbon atoms) is 513/469, perfluoroundecanoic acid (11 carbon atoms) is 563/519, perfluorododecanoic acid (12 carbon atoms) is 613/569, perfluorotridecanoic acid (13 carbon atoms) is 663/619, perfluorotetradecanoic acid (14 carbon atoms) is 713 /669 was measured.
The total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof was calculated using the following formula from the perfluorooctanoic acid content (X) obtained from the above measurement. The detection limit in this measurement is 5 mass ppb.
(A _C4 + A _C5 + A _C6 + A _C7 + A _C8 + A _C9 + A _C10 + A _C11 + A _C12 + A _C13 + A _C14 )/A _C8 x X
A _C4 : Perfluorobutanoic acid peak area A _C5 : Perfluoropentanoic acid peak area A _C6 : Perfluorohexanoic acid peak area A _C7 : Perfluoroheptanoic acid peak area A _C8 : Perfluorooctanoic acid peak area A _C9 : Perfluorononanoic acid peak area A _C10 : Perfluorodecanoic acid peak area A _C11 : Perfluoroundecanoic acid peak area A _C12 : Perfluorododecanoic acid peak area A _C13 : Perfluorotridecanoic acid peak Area A _C14 : Peak area of perfluorotetradecanoic acid X: Content of perfluorooctanoic acid calculated using the external standard method from the measurement results using the MRM method C9-C14 perfluorocarboxylic acid and its salt The content was also measured according to the above.

After reheating in air, 2 to 20 g of a sample was filled in a cylindrical airtight stainless steel container having a PFC content of 50 cc in air, covered with a lid, and heated at 150° C. for 18 hours.
Using 1 g of the heated sample, the PFC content was measured in the same manner as described above.

A powder for measuring the standard value of the absorbance corresponding to the functional group derived from the hydrogen adduct, and a powder obtained in the same manner as the above powder for measurement except that irradiation is performed in the absence of a substance capable of generating a free hydrogen atom. The absorbance was determined by the following measuring method, and the standard value was calculated by the following formula.
Standard value = (absorbance of functional group derived from hydrogenated product of measurement powder) / (functional group derived from hydrogenated product of powder obtained by irradiation in the absence of a substance capable of generating free hydrogen atoms absorbance)
(Measuring method)
The absorbance corresponding to the functional group derived from the hydrogen adduct was measured according to the terminal group analysis method described in JP-A-4-20507.
A low-molecular-weight PTFE powder was preformed by a hand press to prepare a film with a thickness of 0.1 to 1.0 mm. Infrared absorption spectrum analysis was performed on the produced film. Infrared absorption spectrum analysis was also performed on PTFE, which was prepared by contacting PTFE with fluorine gas and the functional groups present in the molecule were completely removed by fluorination. The absorbance height corresponding to the substrate was measured.
The obtained difference spectrum was expanded in the range of 3000 cm ⁻¹ to 4000 cm ⁻¹ and baselined in the range of 3300 cm ⁻¹ to 3970 cm ⁻¹ . At that time, by measuring the height of the peak top at 3556 cm ⁻¹ , the absolute value of absorbance corresponding to the functional group derived from the hydrogen adduct in the PTFE molecule was obtained.

Oxygen concentration in the closed container was measured by analyzing the gas layer in the closed container by gas chromatography. Furthermore, it was confirmed that the oxygen concentration was less than 2.0% by volume (absence of oxygen) by changing the color tone of the oxygen indicator enclosed in the sealed container from purple to pink. Furthermore, it was confirmed with an oxygen concentration meter that the oxygen concentration was less than 2.0% by volume.
Confirmation that the oxygen concentration was less than 0.1% by volume was also performed in the same manner.

Example 1
High-molecular-weight PTFE fine powder (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration below the detection limit A) 20 g was weighed with a weight balance and placed in a bag made of barrier nylon. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 20 g by a weight balance were placed in a bag made of barrier nylon. The high-molecular-weight PTFE and the polyethylene pellets were prevented from coming into contact with each other by providing a partition near the middle of the bag made of barrier nylon so that only the gas could flow. Further, one piece each of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was added to the high-molecular-weight PTFE side and the polyethylene pellet side. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. After confirming the absence of oxygen in the bag by means of an oxygen indicator installed in advance in the bag, the barrier nylon bag was irradiated with 400 kGy of γ-rays. The irradiation conditions at this time were an average dose rate of 6.25 kGy/h at the sample center and a room temperature of 25°C in the irradiation facility.
Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 15 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Example 2
γ-ray irradiation was performed in the same manner as in Example 1. Subsequently, after opening the bag and leaving it open for one day in the atmosphere, only PTFE was put into a 50 mL SUS cylindrical autoclave, and a new oxygen absorber (A-500HS, manufactured by AS ONE Co., Ltd.) was added. was put in and sealed. Next, after repeating the circulation of nitrogen gas and the evacuation by an oil rotary pump three times in the autoclave, the pressure in the autoclave was reduced to 2.7 torr. Heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours using FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech) to obtain low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Example 3
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 2, except that no oxygen scavenger was added to the autoclave.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Comparative example 1
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 1, except that the polyethylene pellets were not placed in a bag made of barrier nylon.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Comparative example 2
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 2, except that the polyethylene pellets were not placed in a bag made of barrier nylon.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Comparative example 3
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 3, except that the polyethylene pellets were not placed in a bag made of barrier nylon.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 1 shows the results.

Example 4
High-molecular-weight PTFE fine powder (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration below the detection limit A) 30 g was weighed with a weight balance and placed in a bag made of barrier nylon. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 15 g by a weight balance were placed in a bag made of barrier nylon. The high molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. After confirming the absence of oxygen in the bag by means of an oxygen indicator installed in advance in the bag, the barrier nylon bag was irradiated with 400 kGy of γ-rays. The irradiation conditions at this time were an average dose rate of 6.25 kGy/h at the sample center and a room temperature of 25°C in the irradiation facility.
Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 23 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). Heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours, 36 hours, 72 hours and 168 hours to obtain low molecular weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 2 shows the results.

Comparative example 4
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 4, except that the polyethylene pellets were not placed in a bag made of barrier nylon.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 2 shows the results.

Example 5-1
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected 30 g (below the limit) was weighed on a weight balance and placed in a barrier nylon bag. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 0.3 g, 1.5 g, 3.0 g, 7.5 g, and 15 g using a weight balance were placed in barrier nylon bags. I put it in. High molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. After confirming the absence of oxygen in the bag by means of an oxygen indicator installed in advance in the bag, the barrier nylon bag was irradiated with 400 kGy of γ-rays. The irradiation conditions at this time were an average dose rate of 6.25 kGy/h at the sample center and a room temperature of 25°C in the irradiation facility. Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 23 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Example 5-2
Example except that high-molecular-weight PTFE fine powder (2) (measured in accordance with ASTM D 4895, standard specific gravity: 2.175, Modified body 1, PFC and PFOA concentrations are below the detection limit) A low-molecular-weight PTFE powder was obtained in the same manner as in 5-1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Example 5-3
Example except that high-molecular-weight PTFE fine powder (3) (measured according to ASTM D 4895, standard specific gravity: 2.168, concentration of modified body 2, PFC and PFOA is below the detection limit) A low-molecular-weight PTFE powder was obtained in the same manner as in 5-1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Example 5-4
Example 5, except that the high-molecular-weight PTFE molding powder (4) (measured according to ASTM D 4895, standard specific gravity: 2.160, homogenate, concentration of PFC and PFOA is below the detection limit) A low-molecular-weight PTFE powder was obtained in the same manner as in -1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Comparative Example 5-1
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected The same operation as in Example 5-1 was performed except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added to 30 g. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Comparative Example 5-2
Polyethylene pellets (Harmony The same operation as in Example 5-2 was performed except that Rex LLDPE, manufactured by Japan Polyethylene Co., Ltd., was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Comparative Example 5-3
Polyethylene pellets (Harmony The same operation as in Example 5-3 was performed except that Rex LLDPE, manufactured by Japan Polyethylene Co., Ltd., was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Comparative Example 5-4
Polyethylene pellets (Harmolex The same operation as in Example 5-4 was performed except that LLDPE (manufactured by Japan Polyethylene Co., Ltd.) was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 3 shows the results.

Example 6-1
A 30 L aluminum bag (inner bag polyethylene) was set in an 18 L can, and polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) weighed to 0.2 kg with a weight balance and an oxygen absorber ( A-500HS, manufactured by AS ONE Co., Ltd.) was put in 15 bags at the bottom of the bag. There, high-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt (PFC) and PFOA The concentration is below the detection limit) was weighed with a weight balance and placed in the aluminum bag. Further, 0.2 kg of the above polyethylene pellets and 10 bags of deoxidizing agents were added, and 2 k of the above PTFE was further added thereon. After repeating this process, a total of 8 kg of PTFE, 0.8 kg of polyethylene, and 50 bags of deoxidizing agents were added. After cooling, the bag was sealed using a heat seal. Each side of the 18-liter can was irradiated with γ-rays of 179 kGy to give a total of 358 kGy. The irradiation conditions at this time were an average dose rate of 6.25 kGy/h at the sample center and a room temperature of 25°C in the irradiation facility. Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 18 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 96 hours to obtain a low molecular weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 4 shows the results.

Example 6-2
A 30 L aluminum bag (inner bag polyethylene) was set in an 18 L 18 L can, and polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) weighed to 0.5 kg with a weight balance and an oxygen absorber ( A-500HS, manufactured by AS ONE Co., Ltd.) was put in 10 bags at the bottom of the bag. There, 1 kg of high-molecular-weight PTFE fine powder (2) (measured according to ASTM D 4895, standard specific gravity: 2.175, modified body 1, PFC and PFOA concentrations are below the detection limit) was weighed on a weight balance. It was weighed and placed in the above aluminum bag. Further, 0.5 kg of the above polyethylene pellets and 10 bags of oxygen absorbers were added, and 1 k of the above PTFE was further added thereon. After repeating this process, a total of 6 kg of PTFE, 3 kg of polyethylene, and 50 bags of oxygen absorber were added. After the inside of the bag was evacuated with an oil rotary pump, the inside of the bag was evacuated (2E-2 torr). Afterwards, the bag was sealed using a heat seal. Each side of the 18 L can was irradiated with γ-rays of 200 kGy to give a total of 400 kGy. The irradiation conditions at this time were an average dose rate of 6.25 kGy/h at the sample center and a room temperature of 25°C in the irradiation facility. Subsequently, without opening the bag, it was stored at room temperature of 20 to 28 ° C. for 2 days (natural deactivation process), and then it was left in the bag without being opened using FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 36 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 5 shows the results.

Example 7
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected 30 g (below the limit) was weighed on a weight balance and placed in a barrier nylon bag. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 15 g, 30 g, 45 g, and 60 g using a weight balance were placed in barrier nylon bags. High molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. The oxygen indicator pre-installed in the bag was pink. The PTFE in the barrier nylon bag is thinly and uniformly dispersed so that it is less than the penetration depth of electrons. Electron beam irradiation of 400 kGy was performed. At this time, moving irradiation was performed, and the absorbed dose with respect to the moving speed was 5 kGy per pass. Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 12 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 6 shows the results.

Comparative example 7
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected A low-molecular-weight PTFE powder was obtained in the same manner as in Example 7, except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added to 30 g. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 6 shows the results.

Example 8
After putting one bag of oxygen absorber (A-500HS, manufactured by AS ONE Co., Ltd.) in each aluminum tray of length x width x height 100 mm x 100 mm x 10 mm, polyethylene pellets (Harmolex LLDPE, Japan polyethylene ( 2g, 4g, 8g, 12g, and 20g of each of these products were weighed with a weight balance and added. On top of that, high-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid having 4 to 14 carbon atoms and its salt (PFC) and PFOA The concentration is below the limit of detection) was added to the top scraping of the tray. The total weight was weighed with a weight balance, the amount of high molecular weight PTFE to be charged was calculated, and the addition rate of polyethylene was determined. This was placed in a bag made of barrier nylon, and the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W) and then sealed by heat sealing. The oxygen indicator pre-installed in the bag was pink. Electron beam irradiation of 400 kGy was performed at 2 MV, 2 mA using a 2 MV electron accelerator (rated 2 MV, 60 kW) manufactured by Nissin Electric Co., Ltd. At this time, moving irradiation was performed, and the absorbed dose with respect to the moving speed was 5 kGy per pass. Subsequently, without opening the bag, it was stored at room temperature of 20 to 28 ° C. for 5 days (natural deactivation process), and then it was left in the bag without being opened. A heat treatment (accelerated deactivation process) was performed at 80° C. for 24 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 7 shows the results.

Comparative example 8
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected A low-molecular-weight PTFE powder was obtained in the same manner as in Example 8, except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 7 shows the results.

Example 9
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected 30 g (below the limit) was weighed on a weight balance and placed in a barrier nylon bag. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 30 g by a weight balance were placed in the bag made of barrier nylon. High molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. The oxygen indicator pre-installed in the bag was pink. The PTFE in the barrier nylon bag is thinly and uniformly dispersed so that it is less than the penetration depth of electrons. Electron beam irradiation was performed at 350 kGy, 400 kGy, and 450 kGy. At this time, moving irradiation was performed, and the absorbed dose with respect to the moving speed was 5 kGy per pass. Subsequently, without opening the bag, it was stored at a room temperature of 20 to 28 ° C. for 12 days (natural deactivation process), and then used as it was in the bag without opening FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 8 shows the results.

Comparative example 9
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected A low-molecular-weight PTFE powder was obtained in the same manner as in Example 9, except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added to 30 g. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 8 shows the results.

Example 10-1
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected 30 g (below the limit) was weighed on a weight balance and placed in a barrier nylon bag. Next, polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 3 g by a weight balance were placed in the bag made of barrier nylon. High molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. The oxygen indicator pre-installed in the bag was pink. The PTFE in the barrier nylon bag is thinly and uniformly dispersed so that it is less than the penetration depth of electrons. Electron beam irradiation of 400 kGy was performed. At this time, moving irradiation was performed, and the absorbed dose with respect to the moving speed was 5 kGy per pass. Subsequently, without opening the bag, it was stored at room temperature of 20 to 28 ° C. for 2 days (natural deactivation process), and then it was left in the bag without being opened using FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). Heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours, 72 hours and 168 hours to obtain low molecular weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 9 shows the results.

Example 10-2
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected Example 10 except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 15 g by a weight balance were placed in the bag made of barrier nylon. A low-molecular-weight PTFE powder was obtained in the same manner as in -1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 9 shows the results.

Comparative example 10
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected A low-molecular-weight PTFE powder was obtained in the same manner as in Example 10-1, except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added to 30 g (lower than the limit). Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 9 shows the results.

Example 11-1
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected 30 g (below the limit) was weighed on a weight balance and placed in a barrier nylon bag. Next, polyethylene pellets (Hermolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) similarly weighed to 1.5 g, 3 g, 7.5 g, and 15 g using a weight balance were placed in the barrier nylon bag. High molecular weight PTFE and polyethylene pellets were mixed in a barrier nylon bag. Furthermore, one bag of oxygen scavenger (A-500HS, manufactured by AS ONE Co., Ltd.) was placed therein. Then, the inside of the bag was evacuated (20 torr) using a vacuum sealer (Fuji Impulse Co., Ltd. V-300-10W), and then sealed by heat sealing. The oxygen indicator pre-installed in the bag was pink. The PTFE in the barrier nylon bag is thinly and uniformly dispersed so that it is less than the penetration depth of electrons. Electron beam irradiation of 400 kGy was performed. At this time, moving irradiation was performed, and the absorbed dose with respect to the moving speed was 5 kGy per pass. Subsequently, without opening the bag, it was stored at room temperature of 20 to 28 ° C. for 2 days (natural deactivation process), and then it was left in the bag without being opened using FORCED CONVECTION OVEN (DRX620DA manufactured by Advantech). A heat treatment (accelerated deactivation process) was performed at 80° C. for 18 hours to obtain a low-molecular-weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Example 11-2
Example except that high-molecular-weight PTFE fine powder (2) (measured in accordance with ASTM D 4895, standard specific gravity: 2.175, Modified body 1, PFC and PFOA concentrations are below the detection limit) A low-molecular-weight PTFE powder was obtained in the same manner as in 11-1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Example 11-3
Example except that high-molecular-weight PTFE fine powder (3) (measured according to ASTM D 4895, standard specific gravity: 2.168, concentration of modified body 2, PFC and PFOA is below the detection limit) A low-molecular-weight PTFE powder was obtained in the same manner as in 11-1. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Example 11-4
Example 11-1 and Example 11-1 except that high-molecular-weight PTFE molding powder (measured in accordance with ASTM D 4895, standard specific gravity: 2.160, homozygous, PFC and PFOA concentrations below the detection limit) was used. A low-molecular-weight PTFE powder was obtained in a similar manner. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Comparative Example 11-1
High-molecular-weight PTFE fine powder (1) (standard specific gravity measured according to ASTM D 4895: 2.171, homogenous, perfluorocarboxylic acid with 4 to 14 carbon atoms and its salt (PFC) and PFOA concentration detected The same operation as in Example 11-1 was performed except that polyethylene pellets (Harmolex LLDPE, manufactured by Japan Polyethylene Co., Ltd.) were not added to 30 g. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Comparative Example 11-2
Polyethylene pellets (Harmony The same operation as in Example 11-2 was performed, except that Rex LLDPE, manufactured by Japan Polyethylene Co., Ltd., was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Comparative Example 11-3
Polyethylene pellets (Harmony The same operation as in Example 11-3 was performed except that Rex LLDPE (manufactured by Japan Polyethylene Co., Ltd.) was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Comparative Example 11-4
Polyethylene pellets (Hermolex LLDPE, Japan The same operation as in Example 11-4 was performed, except that Polyethylene Co., Ltd.) was not added. Various physical properties of the obtained low-molecular-weight PTFE powder were measured. Table 10 shows the results.

Claims (26)

A method for producing a low-molecular-weight polytetrafluoroethylene having a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C., comprising:
a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of a substance capable of generating free hydrogen atoms;
Step (2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating at least part of the main chain radicals and terminal radicals generated by the irradiation in the absence of oxygen.
including
The step (1) is carried out in a substantially vacuum or inert gas atmosphere, or in a closed container,
The method for producing low-molecular-weight polytetrafluoroethylene , wherein the substance capable of generating free hydrogen atoms is at least one selected from the group consisting of synthetic polymers, biodegradable polymers and polysaccharides . A method for producing a low-molecular-weight polytetrafluoroethylene having a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C., comprising:
a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of a substance capable of generating free hydrogen atoms;
The low-molecular-weight product obtained in step (1) is heated or heat-treated at a temperature equal to or higher than the room temperature transition temperature of polytetrafluoroethylene (19° C., which is the dispersion temperature of _β1 ) in the substantial absence of oxygen. step (2a) of obtaining the low-molecular-weight polytetrafluoroethylene by
including
The step (1) is carried out in a substantially vacuum or inert gas atmosphere, or in a closed container,
The method for producing low-molecular-weight polytetrafluoroethylene , wherein the substance capable of generating free hydrogen atoms is at least one selected from the group consisting of synthetic polymers, biodegradable polymers and polysaccharides . The production method according to claim 2, wherein the heating or heat treatment in step (2a) is performed at a temperature of 70°C or higher. A method for producing a low-molecular-weight polytetrafluoroethylene having a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C., comprising:
a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of a substance capable of generating free hydrogen atoms;
The low-molecular-weight polytetrafluoroethylene obtained in step (1) is maintained in an environment substantially free of oxygen for 10 minutes or more after the irradiation is completed , thereby obtaining the low-molecular-weight polytetrafluoroethylene. step (2b)
including
The step (1) is carried out in a substantially vacuum or inert gas atmosphere, or in a closed container,
The method for producing low-molecular-weight polytetrafluoroethylene , wherein the substance capable of generating free hydrogen atoms is at least one selected from the group consisting of synthetic polymers, biodegradable polymers and polysaccharides . 5. The manufacturing method according to claim 4, wherein the holding in step (2b) is performed for 10 hours or longer. A method for producing a low-molecular-weight polytetrafluoroethylene having a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s at 380° C., comprising:
a step (1) of reducing the molecular weight of the high-molecular-weight polytetrafluoroethylene by irradiating the high-molecular-weight polytetrafluoroethylene with radiation in the presence of a substance capable of generating free hydrogen atoms;
Step (2) of obtaining the low-molecular-weight polytetrafluoroethylene by deactivating at least part of the main chain radicals and terminal radicals generated by the irradiation.
and performing steps (1) and (2) simultaneously;
The step (1) is carried out in a substantially vacuum or inert gas atmosphere, or in a closed container,
The method for producing low-molecular-weight polytetrafluoroethylene , wherein the substance capable of generating free hydrogen atoms is at least one selected from the group consisting of synthetic polymers, biodegradable polymers and polysaccharides . The production method according to any one of claims 1 to 6, wherein the amount of the substance capable of generating free hydrogen atoms is 0.0001 to 1000% by mass with respect to the high molecular weight polytetrafluoroethylene. The production method according to any one of claims 1 to 7, wherein the dose of radiation in step (1) is 10 to 1000 kGy. The production method according to any one of claims 1 to 8, wherein the dose of radiation in step (1) is 100 to 750 kGy. The production method according to any one of claims 1 to 9, wherein step (1) is carried out substantially in the absence of oxygen. The production method according to any one of claims 6 to 10, wherein step (2) is performed substantially in the absence of oxygen. The production method according to any one of claims 1 to 11, wherein a substantially oxygen-free state is maintained during the period from the start of step (1) to the end of step (2). The production method according to any one of claims 1 to 12, wherein the high molecular weight polytetrafluoroethylene has a standard specific gravity of 2.130 to 2.230. The production method according to any one of claims 1 to 13, wherein both the high-molecular-weight polytetrafluoroethylene and the low-molecular-weight polytetrafluoroethylene are powders. Before the step (1), a step (3) of obtaining a molded article by heating the high-molecular-weight polytetrafluoroethylene to a temperature equal to or higher than its primary melting point, wherein the molded article has a specific gravity of 1.0 g/ cm ³ or more, the manufacturing method according to any one of claims 1 to 14. ^{Perfluorooctanoic} acid ^and its The salt content is less than 25 mass ppb,
The substance capable of generating free hydrogen atoms is at least one selected from the group consisting of synthetic polymers, biodegradable polymers and polysaccharides ,
The low-molecular-weight polytetrafluoroethylene is a composition having 5 or less carboxyl groups per 10 ⁶ main chain carbon atoms at the ends of the molecular chain. 17. The composition according to claim 16, wherein the content of perfluorooctanoic acid and its salt determined according to the following heating/measurement condition A is less than 100 mass ppb.
(Heating/measurement condition A)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
The content of perfluorooctanoic acid and its salts is measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile is added to 1 g of the heated sample, and ultrasonic treatment is performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase is measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous ammonium acetate solution (20 mmol/L) (B) are fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) is used, the column temperature is 40° C., and the injection volume is 5 μL. ESI (Electrospray ionization) Negative is used as the ionization method, the cone voltage is set to 25 V, and precursor ion molecular weight/product ion molecular weight is measured to be 413/369. The content of perfluorooctanoic acid and its salts is calculated using the external standard method. 18. The composition according to claim 17, wherein the content of perfluorooctanoic acid and its salt determined according to the heating and measurement conditions A is less than 50 mass ppb. 19. The composition according to claim 17 or 18, wherein the content of perfluorooctanoic acid and its salt determined according to the heating and measurement conditions A is less than 25 mass ppb. The composition according to any one of claims 16 to 19, wherein the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof is less than 25 mass ppb. The composition according to any one of claims 16 to 20, wherein the total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof is less than 25 mass ppb. A melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s,
The peak obtained by electron spin resonance measurement under vacuum satisfies the following relational expression (I),
Low-molecular-weight polytetrafluoro having a perfluorooctanoic acid and its salt content of less than 25 mass ppb and a perfluorooctanoic acid and its salt content of less than 100 mass ppb determined according to the following heating and measurement conditions A ethylene.
Relational expression (I): 3.0>Peak M/Peak A>0.3
(In the formula, Peak M represents the peak height at the center of the triplet corresponding to the terminal radical in the low-molecular-weight polytetrafluoroethylene, and Peak A represents the peak height of the double quintet corresponding to the main chain radical in the low-molecular-weight polytetrafluoroethylene. represents the peak height.)
(Heating/measurement condition A)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
The content of perfluorooctanoic acid and its salts is measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile is added to 1 g of the heated sample, and ultrasonic treatment is performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase is measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous ammonium acetate solution (20 mmol/L) (B) are fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) is used, the column temperature is 40° C., and the injection volume is 5 μL. ESI (Electrospray ionization) Negative is used as the ionization method, the cone voltage is set to 25 V, and precursor ion molecular weight/product ion molecular weight is measured to be 413/369. The content of perfluorooctanoic acid and its salts is calculated using the external standard method. A melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s,
The peak obtained by electron spin resonance measurement in the atmosphere satisfies the following relational expressions (1) and (2),
Low-molecular-weight polytetrafluoro having a perfluorooctanoic acid and its salt content of less than 25 mass ppb and a perfluorooctanoic acid and its salt content of less than 100 mass ppb determined according to the following heating and measurement conditions A ethylene.
Relational expression (1): Peak M2/Peak A1≧1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak A1 represents the intensity on the main chain of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the negative peak intensity corresponding to the alkyl-type peroxide radical trapped in ).
Relational expression (2): Peak M2/Peak M3<1.0
(In the formula, Peak M2 represents the absolute value of the negative peak intensity corresponding to the peroxide radical trapped at the molecular chain end of the low-molecular-weight polytetrafluoroethylene, and Peak M3 represents the molecular-chain end of the low-molecular-weight polytetrafluoroethylene. represents the absolute value of the positive peak intensity corresponding to the peroxide radical trapped in ).
(Heating/measurement condition A)
2 to 20 g of a sample is filled in a 50 cc stainless steel cylinder airtight container under the atmosphere, covered with a lid, and heated at 150° C. for 18 hours.
The content of perfluorooctanoic acid and its salts is measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile is added to 1 g of the heated sample, and ultrasonic treatment is performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase is measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous ammonium acetate solution (20 mmol/L) (B) are fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) is used, the column temperature is 40° C., and the injection volume is 5 μL. ESI (Electrospray ionization) Negative is used as the ionization method, the cone voltage is set to 25 V, and precursor ion molecular weight/product ion molecular weight is measured to be 413/369. The content of perfluorooctanoic acid and its salts is calculated using the external standard method. The melt viscosity at 380° C. is 1.0×10 ² to 7.0×10 ⁵ Pa·s, the standard value obtained by the following formula (3) is 1.1 to 10.0, and perfluorooctanoic acid and low-molecular-weight polytetrafluoroethylene having a salt content of less than 25 mass ppb.
Formula (3):
Standard value = (absorbance of functional group derived from hydrogen adduct of low-molecular-weight PTFE)/(hydrogenation of low-molecular-weight PTFE obtained by irradiation in the absence of a substance capable of generating free hydrogen atoms absorbance of functional groups derived from the body) The low-molecular-weight polytetrafluoroethylene according to any one of claims 22 to 24, wherein the total amount of perfluorocarboxylic acids having 9 to 14 carbon atoms and salts thereof is less than 25 mass ppb. The low-molecular-weight polytetrafluoroethylene according to any one of claims 22 to 25, wherein the total amount of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof is less than 25 mass ppb.

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